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Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →BlueDevil Transmission Sealer is a pour-in additive marketed for transmission-fluid leaks, but retailer claims and customer reviews do not establish that it will fix a particular leak. The leak’s source, the transmission’s fluid requirements, and the product’s current label matter before you use it.
What BlueDevil Transmission Sealer claims to do
AutoZone lists BlueDevil Transmission Sealer as part 00236, in a 16 oz bottle. Its product page says the sealer is intended to restore gaskets and seal transmission leaks, describes it as non-clogging and compatible with all transmission fluids, and says it is for manual and automatic transmissions. Those are retailer-presented product claims, not independently verified results. AutoZone also warns that the product is not vehicle-specific and may not fit a given vehicle. Check the current product label and your vehicle’s transmission requirements before use. AutoZone’s BlueDevil Transmission Sealer listing
Directions and dose listed by retailers
AutoZone and Service Champ list the dose as 1 oz per quart of transmission fluid. Service Champ’s directions say to turn the engine off before pouring in the appropriate amount, then drive until leaks are sealed; its catalog listing says this could take up to two days of drive time. Service Champ also warns not to overfill. Service Champ’s product listing
Do not estimate the amount based on the bottle size or add fluid without checking the transmission’s specified capacity and procedure. An overfilled transmission can create its own problems. Confirm whether the additive is appropriate for your specific transmission and fluid, and follow the current package label rather than relying solely on retailer directions.
#1 Best Overall
- Permanent Transmission Leak Repair: Seals leaks in automatic and manual transmissions
- Restores Rubber Seals: Revitalizes dried, cracked, and shrunken seals
- Non‑Clogging Formula: Safe for internal transmission components
- All Fluid Compatible: Works with all transmission fluid types
- Easy Pour‑In Application: DIY solution that works while you drive
Why the leak’s source matters
A transmission-fluid leak can come from different places, and an additive marketed to address gasket leaks cannot be assumed to repair every source. The cited listings do not establish that this sealer fixes a particular leak, such as one from a damaged line, a loose connection, a cracked component, or a failed seal. A leak’s location and cause need to be identified before choosing between an additive and a mechanical repair.
If the leak is worsening, the fluid level is dropping, or you are unsure whether the fluid is transmission fluid, arrange an inspection instead of relying on a stop-leak product. Delaying diagnosis can leave the underlying fault unresolved. A vehicle-specific repair can only be selected after confirming the leak source and the vehicle’s fitment requirements.
Rank #2
- Easy to use: The BlueDevil Oil Stop Leak is designed to be easy to use, simply pour the recommended amount into the leaking component’s oil slump, or crank case.
- Permanent seal: BlueDevil offers a permanent solution with our Engine Oil Stop Leak that is proven to seal your leak and get you back on the road again. Formulated to stop your seeping or dripping oil leaks permanently and keep your leak sealed even after miles of driving.
- Compatible with all types of engines: Compatible with gasoline and diesel engines, making it a versatile product that can be used on a wide range of vehicles.
- Versatile Uses: Repairs and reconditions rubber seals throughout any fluid oil system. Can be used for pinion seals, gear cases, refillable shock absorbers, gear boxes, axle seals, and gear differentials.
- Safe to use: Designed with a non-clogging formula that won’t temporarily swell seals. Does not contain petroleum and is not harmful to your engine
What customer reviews can—and cannot—tell you
When accessed in 2026, AutoZone displayed a 3.7 out of 5 rating from 166 ratings. Some reviewers reported that a leak slowed or stopped; others reported no improvement or a worse leak. These are mixed, self-reported accounts, not controlled tests. They cannot establish that the additive caused a reported change, provide a reliable success rate, or predict whether it will work on a specific vehicle or leak.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Safety and handling
A Universal Products, Inc. safety data sheet dated July 17, 2014 identifies the product’s use as an automotive transmission gasket sealer and classifies the mixture as a combustible liquid and harmful if swallowed. It describes a proprietary ingredient above 90%, with exact identities and concentrations withheld as trade secrets. Because that sheet is dated, it does not confirm the current formula or hazard labeling. The 2014 BlueDevil Transmission Sealer safety data sheet
Rank #3
- STOPS LEAKS, SLIPPING AND ROUGH SHIFTING: Reduces rough shifting and friction, while eliminating slip, controlling temperature, and repairing shudder, chatter and whining.
- RESTORES PERFORMANCE: Premium high mileage formula restores transmission performance and saves on costly transmission / transaxle repairs.
- FLUID STABILIZER: Use when topping off existing fluid when low, or add a bottle when changing the fluid.
- SEALS CONDITIONERS: Stops leaks, slipping and rough shifting. Reduces heat & friction, and stabilizes fluid.
- REPAIR IT: Transmission Repair-It works with all types of transmission fluids
Service Champ advises avoiding skin contact, wearing protective eyewear, keeping the product away from children, and not using it in brake systems or on painted surfaces. Follow the current bottle label and safety data sheet for handling and disposal instructions; the distributor listing advises following local, state, and federal disposal rules.
Quick Recap
Rank #4
- Stops Leaks
- Helps prevent wear and corrosion
- Improves vehicle longevity and performance
- Smooths and eases steering operation
- Helps prevent slippage
Questions to answer before using it
- Has the leak been identified as coming from a transmission gasket or another source?
- Does the current product label approve use with your transmission and specified fluid?
- Do you know the correct fluid capacity and application procedure for your vehicle?
- Is the leak stable, or is it worsening enough to warrant prompt diagnosis rather than waiting for an additive?
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
