10 Best Transmission Additives 2025 in the United States

The ATP Automotive AT-205 Re-Seal is a specialized additive designed to stop leaks by rejuvenating rubber seals and gaskets in transmissions, engines, power steering, differentials, and hydraulic systems. It works well with both conventional and synthetic oils, including automatic transmission fluid (ATF) and gear oils, making it versatile for various vehicle systems. One of its strengths is that it doesn’t contain petroleum distillates, so it won’t cause seals to over-swell or break down, which helps extend the life of your vehicle’s seals without damaging them.

The product comes in an 8-ounce bottle, enough to treat up to 6 quarts of fluid, fitting typical maintenance needs for many cars. However, the bottle size and weight indicate it’s a compact treatment, so for larger systems or repeated use, you may need to adjust the amount accordingly. While it’s mainly aimed at stopping leaks quickly and effectively, it may not replace the need for professional repairs if the damage is severe.

For those looking for a straightforward, easy-to-use additive to maintain the integrity of rubber seals in their vehicle’s transmission and related systems, the ATP AT-205 provides a reliable and safe option.

The Valvoline DEXRON VI/MERCON LV ATF is a full synthetic automatic transmission fluid designed to work with a wide range of vehicles requiring DEXRON VI or MERCON LV specifications. It uses advanced additives and synthetic base oils to provide smooth shifting, reduce shudder, and protect the transmission from wear and heat damage. This fluid flows well even at low temperatures, ensuring better performance in cold starts, while maintaining a strong protective film at high temperatures.

Its viscosity and additive concentration are optimized for durability and efficient power transfer, making it a solid choice for anyone looking to improve their transmission's lifespan and function. It is formulated specifically for automatic transmissions needing these particular specs, so confirming compatibility with your vehicle before use is important. Positive user feedback supports its reliability and effectiveness. The one-gallon bottle size is convenient for both topping off and full transmission changes.

The LIQUI MOLY Automatic Transmission Fluid (ATF) is a strong choice for BMW owners seeking reliable transmission lubrication. With a volume of 6 liters, it’s sufficient for various maintenance tasks without requiring a core charge, making it user-friendly. One of its strengths is its compatibility with BMW vehicles, ensuring it meets the specific needs of those models.

In terms of performance, the viscosity rating of 2.85 mPas at 100 degrees Celsius suggests it will maintain adequate lubrication and flow at a range of temperatures, which is critical for transmission health. Liqui Moly is a reputable brand in the automotive field, known for producing high-quality oils and additives, further reinforcing confidence in this product.

While the product is tailored for BMWs, it may not be suitable for other car brands, potentially limiting its appeal for broader audiences. Additionally, the liquid volume, while ample for many purposes, may be excessive for individuals who only need a small amount for a single maintenance job, leading to potential waste if not used entirely.