Best Transmission Stop Leak


A leak can starve your transmission of the fluid that cools and lubricates vital internal components. If ignored, a leak can cause the transmission to run low on fluid, resulting in severe damage. Then, the transmission will either need to be rebuilt (if possible) or replaced. It’s never a good idea to drive your vehicle with your transmission fluid below the minimum level. Adding a bottle of one One Seal Stop Leak or Transmission Seal Stop Leak products is often all it takes to seal your leak. Then all you have to do is check your transmission fluid level.

  1. Whats The Best Transmission Stop Leak
  2. Best Transmission Stop Leak Reviews
  3. Transmission Leak Repair

It’s common to experience hard shifting or slipping transmission issues that beg your attention to solve it. If you didn’t know, a faulty transmission can leave a big hole in your pocket the size of a crater. But wait! There is an easier and affordable solution that doesn’t involve replacing the transmission system. A transmission fluid additive makes it possible to reduce friction, overheating, leakage and clogging issues. However, instead of just jumping in blindly, we’ve reviewed some of the best transmission stop leak additives currently available.

Product Type Specialty Size Shelf Life
Hot Shot's Secret Transmission Restore AdditiveAutomatic and CVTFix slipping transmission32 Oz5 years
LUCAS Transmission FixAutomatic and ManualFix slipping transmission24 Oz5 years
Sea Foam Trans Tune Transmission AdditiveAutomatic Fix sticky valves16 Oz4 years
Prolong Super Lubricants PSL15000 Transmission TreatmentAutomatic and manual Fix slipping transmission8 Oz5 years
Lubegard 19610 Instant Shudder FixxAutomatic Shudder reduction2 Oz2 to 4 years
XADO Revitalizant EX120Automatic and CVT/ Manual Shudder reduction 0.28 Oz2 to 4 years
zMax 51-306 Transmission FormulaAutomatic and ManualFix slipping transmission6 Oz5 years
Bar's Leaks 1400 Transmission RepairAutomatic Fix slipping transmission and noisy engine16 Oz5 years

Hot Shot’s Secret Transmission Restore Additive

A transmission additive suited for both automatic and CTV transmission systems.

Type: Automatic and CVT Speciality: Fix slipping transmission Size: 32 Oz Shelf Life: 5 years


  • Slows down friction and tear
  • Large 32-ounce bottle
  • Compatible with automatic and CVT engines
  • Prevents rust and corrosion
  • 5 years lifespan


  • Not ideal for manual transmission systems
  • Limited to fixing minor hard shifting issues.

Looking for an additive that can handle both automatic and CTV transmission systems? The Hot Shot’s Secret Transmission Restore Additive may be your best gamble.The ingredient formula is multi-purpose since it can reduce friction, prevent overheating and act as a protective layer to keep off rust and corrosion.

Quite impressive, it comes packed in a big bottle with a lifespan of 5 years. What else? It lubricates the metal parts for a smoother gear shift, plus it attracts deposits off the coated areas. In other words, the performance of your automatic and CTV transmission will be top-notch and the transmission system will probably last longer if you apply this product.

Its biggest disappointment is that it can’t be used for manual transmission systems. Moreover, it can only fix minor hard shifting issues but if the transmission system is too damaged, it won’t do much. But then again, transmission stop leak additives are intended for a temporary quick fix.

LUCAS Transmission Fix

A formula with no solvent to stop leakage and regulate temperature.

Type: Automatic and Manual Speciality: Fix slipping transmission Size: 24 Oz Shelf Life: 5 years


  • Prevents foaming
  • Stops transmission leaks
  • It can be added straight into the regular fluid
  • Contains no solvents
  • Regulates operating temperature
  • Cheap


  • It doesn’t work well with extremely damaged transmission systems
  • Not ideal for CVT transmissions

Most seasoned mechanics will recommend the Lucas Transmission Fix to sort out your leakages and hard shifting problems. That is because this product is cheap yet it can deliver better results than most premium products. How is it so? It stops leakage, regulates operating temperature and recharges worn out transmission fluid.

The formula contains no solvent whatsoever but it is capable of preventing foaming. In fact, you won’t even need to drain the transmission fluid to add it since you can pour it directly. In addition to that, it can be used on both manual and automatic transmission.

Despite being regarded as one of the best transmission additives on the market, this product is not ideal for CVT transmissions. Beyond that, don’t expect it to do miracles on extremely damaged or worn out transmissions systems. Sure, it can keep your transmission system together for a few days but if it is too far gone; it can only perform to its limitations.

Sea Foam Trans Tune Transmission Additive

It features a patented formula to remove water residue and clean sticky valves.

Type: Automatic Speciality: Fix sticky valves Size: 16 Oz Shelf Life: 4 years


  • Compatible with automatic transmissions
  • Eliminates moisture and deposits
  • It can be used in hydraulic pumps and power steering
  • Doesn’t change the viscosity of the transmission fluid
  • Cleans sticky valves


Whats The Best Transmission Stop Leak

  • Not suitable for manual transmissions
  • Packed in a small bottle

When was the last time you came across a transmission stop leak additive that removes moisture? Apparently, the founder of Sea Foam products worked on boat motors and that is why this additive contains a patented formula to remove water residue better than other additives on the market. It can also eliminate deposits and clean sticky valves.

For what it’s worth at a cheap price, it is multi-purpose to service automatic transmissions, power steering, and hydraulic systems thanks to the petroleum-based formula. The ingredients don’t change the viscosity of the transmission fluid or swell the seals. If you have a rough or erratic shifting issue in your vehicle, the additive will dissolve varnish to free the pumps and passages.

Unfortunately, the Sea Foam Trans Tune Transmission Additive isn’t suitable for manual transmission systems. On top of that, it is packed in a smaller than average bottle which means it won’t last long unless you buy extra bottles.

Prolong Super Lubricants PSL15000 Transmission Treatment

A manual and automatic that can restore your transmission system.

Type: Automatic and manual Speciality: Fix slipping transmission Size: 8 Oz Shelf Life: 5 years


  • Anti-friction technology
  • Enables smoother shifting
  • Compatible with both manual and automatic transmissions
  • Protects against overheating
  • Effective under intense pressure


  • Not ideal for CVT transmission systems
  • Small bottle
  • Less effective on high mileage trucks and SUVs

For those who have both manual and automatic vehicles in their garage, this additive can fix either of your machines. It will save you money too. Anyway, it entails a special patented formula that interacts with the metal parts of your transmission system at a molecular level to create a protective bond to shield against friction and excess temperature.

A single bottle is 8 ounce but it is enough to reverse your transmission system back to its former glory. It enhances smoother and faster responsive gear changes. Even during intense pressure conditions, it will still deliver regardless of whether it is operating in low or high mileage cars.

It turns out, this transmission additive is not ideal for CVT transmission systems. The bottle is small, which means you need to buy two bottles separately if you have two vehicles. There have also been cases where it less effective on high mileage trucks and SUVs.

Lubegard 19610 Instant Shudder Fixx

It is one of the most popular transmission fluid additives due to its extra protection features.

Type: Automatic Speciality: Shudder reduction Size: 2 Oz Shelf Life: 2 to 4 years


  • Promotes stable fluids
  • Prevents overheating
  • Solves transmission shudder problems
  • Prolongs transmissions system lifespan
  • Reduces friction


  • Not compatible with manual or CTV transmission systems
  • Very small bottle

At first, you may think it is a marketing gimmick when you find out that Lubegard 19610 Instant Shudder Fixx was voted the top stop leak additive product by transmission professionals. However, it deserves the bragging rights since it’s one of the most popular transmission additive fluids on the market.

What makes it so good? It offers four times better protection than the regular automatic transmission fluid. The concentrated solution is purposely designed to promote stable fluids and restore your shaking engine to normalcy. Of course, for such a popular transmission additive, it reduces friction and balances the internal temperatures.

On the downside, it is not ideal for CVT transmissions, Ford type F and manual transmission. Otherwise, it can work just perfect with any automatic transmission system. Another thing; the 2-ounce bottle is very small for multiple uses. But then again, quality over quantity.

XADO Revitalizant EX120

It is compatible with both CVT and transmissions, plus there is an alternative formula for manual transmissions.

Type: Automatic and CVT/ Manual Speciality: Shudder reduction Size: 0.28 Oz Shelf Life: 2 to 4 years


  • Compatible with CVT and automatic transmissions
  • Reduces noise and stops vibration
  • Protects against extreme temperature
  • Prevents transmission shudder
  • Substitute formula for manual transmissions
  • Anti-friction modifier
  • Fast-acting formula
Automatic transmission stop leak reviews


  • Higher price than other products
  • Small dosage

Okay, the guys who own vehicles with CVT transmissions must have been fed up by now. For that reason, we included XADO Revitalizant EX120 in this guide because it is compatible with both CVT, automatic and semi-automatic transmissions. As a matter of fact, it is one of the few complete universal transmission stop leak additives on this guide since you can choose a substitute formula for manual transmission.

The formula is inserted through an 8 ml syringe hence it requires a lot of precision. Like most top-quality transmission additives, it can protect against extreme overheating, reduce noise, friction and stop annoying engine vibrations. In other words, it is the ultimate formula to prevent transmission shudder for any type of vehicle. Mind you, it is a fast-acting additive and it can restore your transmission system in less than 72 hours.

It is almost flawless except you would have to pay a higher price compared to other products. The process of topping up your transmission fluid can be a little challenging if you’re a beginner. Watch out if you have shaky hands. To your advantage, there are clear instructions prescribed on the bottle of how you should apply.


zMax 51-306 Transmission Formula

It’s great for reducing contamination and preventing fluid leakage.

Type: Automatic and Manual Speciality: Fix slipping transmission Size: 6 Oz Shelf Life: 5 years


  • Ideal for both manual and automatic transmissions
  • Improves shifting
  • Lubricates to reduce friction
  • Prevents wear and tear
  • Seals leakage


  • Not suitable for CVT transmission system
  • Small bottle

How about an additive that you need to apply at least once per year? This product is designed to fix those slipping transmission issues on both manual and automatic gear vehicles. Its primary purpose is to stop fluid leakage and reduce contamination within the transmission system to enhance performance.

The molecules within the solution are smaller than the typical trans fluid, hence it alters the internal metal parts of the transmission by reducing varnish, sealing the leaks and controlling the temperature. Beyond that, applying it is easy since you won’t need to drain the transmission fluid.

Like most additives that are compatible with both manual and automatic transmission, this product is not intended for CVT transmissions. Also, the 6 ounces bottle is smaller than average but on the bright side, you only need to top it up once in a blue moon.

Bar’s Leaks 1400 Transmission Repair

A budget friendly automatic transmission fluid additive to fix slipping transmission issues.

Type: Automatic Speciality: Fix slipping transmission and engine noise Size: 16 Oz Shelf Life: 5 years


  • Affordable
  • Improves performance
  • Reduces engine noise
  • Conditions O-rings and seals
  • Prevents rough shifts
  • Controls the temperature
  • Quick response time


  • Not compatible with CVT and manual transmission systems

If you are having a rough shifting, chattering or whining issues in your automatic engine, it’s time to consider buying the Bar’s Leaks 1400 Transmission Repair to fix the problem. For this product to do that, it must reduce friction, control the internal temperature and stabilize the fluid. Further, it is designed to condition the seals and O-rings to restore your vehicle’s A-game.

Applying the transmission additive is easy because it is designed to work with all kinds of transmission fluid. All you need to do is check the dipstick and pour the contents directly if the fluid level is low. Keep in mind that you will have to drive for at least 2 days before you notice the results.

The manufacturers don’t recommend it to be used on CVT or manual transmission systems. To achieve the desired results, you will most likely need to use a whole bottle; although, you can purchase a pack of four to save for a rainy day. Regardless, it is one of the most affordable and top-quality transmission additives on the market.

Why Should You Buy a Transmission Stop Leak?

  • Stop Transmission leaks. It’s obvious, isn’t it? Let’s face it, most transmission systems wear out after hitting the road for years. Whatever follows next is usually a leakage problem that can slow down your engine’s performance and even corrode the metal components. A transmission additive gives you a chance to stop the leak before it spreads out. Metaphorically speaking, sealing a crack before it brings down the wall.
  • Reduce engine noise. Ever heard that annoying and loud noise from your engine when you start it? It sounds like clanking and whirring noise. Sometimes, you may experience vibrations and shifting difficulties. The message couldn’t be more clear; that is a symptom of a worn-out transmission system probably low on fluid. A transmission stop leak additive can fix that issue.
  • Prevents varnish and clog effect. Inevitably, the transmission fluid becomes contaminated and gets thicker after prolonged use. The lubrication decreases after the fluid stops flowing effortlessly and varnish start to form. If it keeps on going for long, the transmission will clog due to the contamination. A transmission stop leak additive can act as a fluid treatment that prevents the varnish and clog effect.
  • Maintains the engine’s performance. When you buy a brand new car, theengine’s performance is at its peak. Gradually, the transmission fluid ages and sludge forms forcing the engine to work harder. Next, the transmission system is overwhelmed and the engine’s performance slows down. Do you see where we’re going with this? A transmission additive could be your best bet.
  • Saves You Repair Money. A worn out and clogged transmission system willsuck your money like a vacuum cleaner. What’s worse, leaking transmission fluid is corrosive and it can damage crucial components of your engine. The solution? If you use a transmission additive with the right formula, you will prevent the engine from overheating; which in turn improves fuel efficiency and shifting. Also, it prolongs the lifespan of your transmission system and saves you money. Now that’s what we call killing two birds with one stone!

Basic Types of Transmission Additives

Manual Transmission Additive

Manual transmission additives are made with a formula that prioritizes high viscosity and high heat resistance. This is because manual gears come with a two-shaft system that produces intense heat and friction whenever the shaft gears collaborate. Hence, manual transmission additives are designed to operate under extreme pressure without losing the composure that would otherwise damage the engine components.

Automatic Transmission Additive

Unlike a manual transmission, automatic transmissions use a planetary system which enables the gears to switch automatically in sequence to the commands of the engine. Moreover, automatic gears are typically smaller than a manual gearbox, but with more moving parts. For that reason, automatic transmission additives tend to have a lower viscosity than manual additives. Instead, the focus is on anti-foaming, cleaning and heat resistance.

Universal Additive

As the name suggests, a universal additive is used for both automatic and manual transmissions. If you got two or more vehicles with different transmissions in your garage, you could buy a universal additive and save some money. Universal additives are heat resistant and they can prevent foaming and fluid oxidation. Other patented universal transmission stop leak formulas help to tighten the shift cycle and extend the transmission fluid’s longevity.

CVT Additives

Compared to automatic transmissions, continuously variable transmissions (CVT) are engineered with a belt or chain-driven maneuver. That means CVT transmissions are expensive to repair than automatic transmissions; because they’re more specialized and sophisticated. To prevent damage, CVT additives are formulated to prevent shudder and slipping problems that would negatively affect the performance.

So Which Is The Best?

Frankly, it all depends on the transmission system of your vehicle. Suffice to say, if you’re driving a car with an automatic transmission, you won’t do yourself a favor if you opt for a manual transmission stop leak formula. The modus operandi should be to stick to additives purposely designed for your engine with the exception of universal additives.

Other than that, if you want the best transmission additive, you should pay more attention to the formula and what it could do.

Highest Rated Transmission Additive Brands

Lucas Oil

C’mon, who hasn’t heard of Lucas Oil? It is one of the world’s most popular manufacturers and distributors of transmission additives. The company was founded in 1989 and currently, it supplies its products to more than 40 countries.


ProLong Super Lubricants

Just like Lucas Oil, ProLong Super Lubricants was founded in 1989. Due to their high-performance lubricants, ProLong lubricants eventually became one of the most-sought out automobile fluid additive brands in North America. Its most critically acclaimed transmission stop leak product is Prolong Super Lubricants PSL15000 Transmission Treatment.

Hot Shot’s Secret

The brand is known for creating additives that solve specific problems related to diesel and gas engines. It is for that reason why its parent company, Lubrication Specialties Inc., has worked with some of the biggest companies in North America such as X-Tec, Nucor Steel, Midwest Industries and American Showa. Its most popular transmission additive is Hot Shot’s Secret Transmission Restore Additive.

How to Choose the Best Transmission Additive


As mentioned earlier, you need to choose a suitable transmission stop leak fluid additive based on the transmission system. For instance, a manual transmission additive should be used on a manual transmission system. If you’re not sure about the transmission system of your vehicle, you ought to consult the vehicle’s owner’s manual.


Ask yourself; what transmission issue do you want to solve? If your engine is making a lot of noise, it would be logical to opt for an additive with a formula designed to reduce noise. Of course, other formulas can reduce friction, prevent overheating and cut off oxidation. Whatever your options, the best transmission additives are the ones that include a formula diverse enough to tackle all transmission related issues.


Transmission fluids are either natural or synthetic. The most popular transmission fluid on the market is synthetic. Nevertheless, you should confirm the type of transmission fluid (synthetic or natural) your engine uses before buying an additive. The fluid type is usually written on the bottle’s instructions or ingredients list.

Bottle Size

You don’t want to keep running out of transmission additive, do you? Well, the bigger, the better. Besides that, do a quick math on the economies of scale. Apart from having a large bottle that can be utilized many times, you will save money since you won’t be running back to the store. Did I mention, there are transmission additives that have a shelf life of around five years?


In most cases, cheap is expensive and if you go the lowest-priced transmission stop leak fluid on the market, don’t be surprised if you get a knock-off. The good thing is, most transmission additives are sold for under $30. A little secret when you’re not certain of the brand’s reliability is to check the reviews.

How to Add Transmission Additive

Now let’s get our hands dirty! Adding the transmission additive depends on the brand or type of additive. While some additives will require you to remove the dipstick and pour directly into the regular fluid through a funnel, others could instruct you to drain the transmission fluid before balancing it with the additive. That’s why, folks, you should always read the instructions (both on the vehicle’s manual and additive bottle).

Whatever the case, topping up the transmission fluid should only take you a few minutes. Afterward, you can drive out to analyze the gears. Keep in mind that some transmission treatments can take up to 48 hours to be effective.

Final Thoughts

One thing is for sure; all the transmission stop leak additives mentioned in this article are currently the best you could find. Not to take it away from the others, but after thorough analysis, we think our winner would be a tie between LUCAS Transmission Fix and XADO Revitalizant EX120. That’s because both transmission additives are versatile to handle both automatic and manual gear systems.

Are you having trouble with your transmission system? Please share your experience and we would be glad to give you a recommendation.

You May Also Like:

Best Transmission Stop Leak Reviews

James Dolan is an automotive expert and a freelance writer. Anything new in the automotive industry? James Dolan will tell you about it. When he’s not working, you can find him playing hockey, traveling or hanging out with his German Shepherd Dog.

Transmission Leak Repair

ATP Automotive Re-Seal Stops Leak

ATP Automotive is the best transmission leak sealer that performs well and can be used for stopping other leaks. It works quickly and effectively in stopping all leaks in the transmission. We also it for its value for the dollar.

Having a leak in your transmission is quite annoying. When it happens, you will see oil drips here and there, and you will lose 3 quarts of oil per month at least. There will be a lot of expensive and frustrating problems if the transmission fluid goes too low. It causes higher transmission temperature, and makes the friction components wear faster. You may seriously damage your transmission if you keep driving with a low fluid level. Therefore, you should stop the leak as soon as possible if you want to maintain your vehicle in good condition.

To solve the transmission leak problem, you must choose carefully. There are dozens of products for different oil leak problems, but most of them are not professionally designed for transmission leaks. They may be helpful, but are not very effective. The reason is that the rubber parts in transmissions are different with those in other oil systems. They need different components to get restored.

If you want to get the best performance, here are 5 products we highly recommend. They are fast, convenient and good value for money. These 5 products are the best transmission leak sealers on the market, and you should have one around the garage on in your car.

ATP Automotive Re-Seal Stops Leak

When you notice that your car has a transmission leak, it may not be the only problem. Damaged parts in engines, power steering, differentials and hydraulic systems may also cause leaking problems. You need something to stop the leak and prevent other kind of leaks in the future. We recommend ATP AT-205. It is the best transmission oil stop leak in terms of performance. ATP AT-205 can quickly stop transmission leaks. According to our tests, ATP AT-205 completely stopped the leak after driving about 800 miles. It restores all rubber seals and gaskets in the transmission, and brings them back to their best conditions.

ATP AT-205 also helps to prevent future leaks. It works not only in transmissions, but also in engines, power steering, differentials and hydraulic systems. It restores all rubber parts just like it has done in transmissions. ATP AT-205 is compatible with most kinds of oils on the market. So, it performs the same in different oil systems and does no harm to components.

It’s easy to use ATP AT-205. When you are going to do the oil change, drain some waste oil and pour a full bottle in. Let it circulate in the system, and usually you will find that the leak stops after a total of 5 hours of driving. The product may not work if the leak is caused by metal parts. In that case, you can call the manufacturer for further help.

Lucas 10009 Transmission Fix

Lucas is one of the most well known producers of transmission leak sealers. They produce dozens of products for different oil leaks. The Lucas 10009 is the best transmission oil leak stop additive in their lineup. As we investigated, Lucas 10009 solves most of the transmission leak problems, and it has been widely approved by its customers.

Lucas 10009 is quite popular because it stops transmission leaks fast. The transmission leaks are usually caused by dried-out, harden or shrunk rubber parts in transmissions. Lucas 10009 can quickly restore them and bring them back to their best conditions. In this way it stops the leak permanently and also prevents the future leaks.

Lucas 10009 is also easy to use. It is suitable with all kinds of oils, so you don’t have to drain any fluid before adding Lucas 10009. It contains no solvents, so it’s harmless and you can use it in most kinds of oil systems. You can’t be wrong if you follow the instruction. Add a full bottle of the product in, and you will get a no-leak vehicle after a few hours of driving. You should do it every 5000 miles, so it will prevent leaks in the future.

Sometimes Lucas 10009 doesn’t work because the vehicle are too old to fix. It can’t restore the torn metal parts, or the rubber parts which are broken into pieces. In this situation, you should take your vehicle to the garage and let skilled workers fix it.

We can’t ask for more since Lucas 10009 is just a cheap solution for transmission leak problems. But we can get a lower price if we buy it by the dozens. It won’t waste your money because you will use it very often as a good measure of daily maintenance.

BlueDevil Transmission Sealer

If you are familiar with transmission leak sealers, you must know BlueDevil Products. It’s well known as it has produced dozens of products for all kinds of oil leaks. Most products of this company are proved to be effective, and BlueDevil Transmission Sealer is the best transmission leak sealer of BlueDevil Products.

BlueDevil permanently stops the leak in transmissions. The dried, cracked and shrunken rubber seals will be restored by BlueDevil, and they will no longer cause transmission leaks. It works in manual or automatic transmissions. You will see the difference after using no more than two bottles of the product. Otherwise, it is a leading indication that you have serious problems with your transmission. In that case, you should ask the manufacturer or some skilled worker.

If your transmission doesn’t leak, you can also use BlueDevil to prevent future leaks. You don’t need to worry because it doesn’t harm the transmission or any other parts of the oil system. To get the best performance, you should add a full bottle of the product in the oil right before the oil change. It will restore rubber seals and gaskets after circulating in the oil system.

Motor Medic Automatic Transmission Sealer

Motor Medic M1432 is the best transmission oil leak stop provided by MotorMedic. The company is well known because of the good quality of its products. Just like other MotorMedic products, Motor Medic M1432 is reliable and convenient. It works great on stopping transmission leaks, and it’s helpful to prevent future leaks.

Motor Medic M1432 does a great job with transmission leaks. Like its competitors, Motor Medic M1432 restores rubber parts which are dried, harden or shrunk. It performs the best when working on the seals and gaskets in transmissions. It may not be effective if the leak is caused by torn metal parts. You should carefully check your transmission before using this product, or it would be a waste of money.

Motor Medic M1432 is convenient. All you need to do is add it right before oil changes. The leak will be stopped after several hours of driving. It won’t damage your transmission, and you can mix it with any other kind of oils. Finally, Motor Medic M1432 is quite cheap. It’s definitely worth a try. It’s not a big deal if it fails to stop the leak as it can still prevent future leaks.

Bar’s Leaks Transmission Stop Leak

Bar’s Leaks 1420 may be one of the best transmission stop leaks on the market. Sophos threat. It may not be as effective as other professional products, but it performs well when solving transmission leak issues.

Bar’s Leaks 1420 restores gaskets and seals to stop transmission leaks. Usually, it takes an hour to completely stop the leak. The bad thing is, its performance is extremely fast but not very stable. This product is specially designed for transmissions, and it may do nothing if the rubber parts are not suitable. It sometimes fails when working on super old cars. We advise you not use Bar’s Leaks 1420 as the first attempt to fix old leaks. You should use it as a weekly maintenance for your transmission.

To get the best performance, you should read the instruction or call the manufacturer before using Bar’s Leaks 1420. If your transmission is suitable, the product will work well and fast.