[mowowie]

The difference between a tranny and an engine is that no combustion occures in a transmission.
No un-burned gasoline, oxidation, or other contaminates ever enter a transmissions case.
As long as the transmission operates properly The oil remains the same for most of it's life.

[Hillarys Gate Cult]

Odd thing I found is that a Honda CRV will get oxidation in it's differential and eventually sound like a bad CV joint unless the fluid is changed. It's the only vehicle I have ever heard of doing that.