KTLIMQ, that article about the Dexron III vs VI seems to make sense.
Do ATF fluids lose viscosity during use? I understood that multi-weight traditional motor oils became thicker with use, due to the loss of the lighter, more volatile molecules. That is supposed to be one of the big advantages of synthetic motor oil. But, I never thought about ATF changing viscosities one way or the other.

As my old '91 tranny aged, I sitched to the Valvoline Max Life ATF, supposedly designed for older cars, it is supposed to have additional seal conditioners and a bit more viscosity - yada, yada. So far, so good, I have had zero leaks - but I did wear out the reverse clutch plates. Probably not related.

DG