For the most part, I’m not a fan of additives. Most of them have compounds that voraciously attack the “rubber” seals throughout the transmission. Usually, only a portion of the seals have hardened due to heat and age, but the additives will not be able to differentiate between the ones that are hard and the ones that aren’t.
Therefore, when the additives come in contact with the seals, they swell and soften to a point that they will not function. The common experience after using the additive is a betterment initially, but after a few weeks, there is a major deterioration in the performance of the unit. If the seals are damaged, there is no improvement, just the deterioration phase.
With external leaks, the additive will not cure gaps, such as loose pump bolts, worn bushings, cracks in the case, bad gaskets, etc.
I’ve seen more harm than good from the use of such products, and am a firm believer in periodic service as the best for the health of the unit.
The only one that we will use is called “Lubegard,” and is used primarily the cure minor valve body hang-ups and torque converter clutch chatter.
If all those additives for sale did as much as they promise, we would not be in business!
Also, usually the slickest thing about the additive is the person selling it!