"additional seal conditioners" in most transmission stop-leak formulas and "high mileage" ATFs are naptha, benzene, "petroleum distillates", acetone, ... any solvent that softens rubber. Not good for the long-term, but can extend the life of a failing transmission's seals.

I've heard of everything from brake fluid to acetone added to a transmission to make it shift when (internal) seals are leaking too much to have adequate control pressure at idle.

Best to just run good ATF if your only leak is external IMO, cardboard is cheap.

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Gone to the dark side

- Jeff