Originally Posted By: Olas
Do it every 2 years or 30k miles, whichever comes first.
a pan drop every 2 years? a filter change every 2 years? how much metal do the automatic transmissions you have experience with shed? sounds problematic, you would introduce more dirt by doing it so often, just like an air filter system, constantly checking introduces more dirt then leaving it alone.
OP, as far as Toyotas(Corolla/Celica/Camry) are concerned I have seen original ATF with 100-250k miles on them, those work perfectly fine before and after a pan drop.
I think a pan drop w/ filter change every 100-120k is good, now a drain & refill every 30k(I'm personally doing 60k), or you could do as often as you like but it would be a waste of money unless you have a problematic transmission.