My pan stays on until something's wrong..... which shouldn't be very often.........Then it gets a new gasket when I buy an overhaul kit.....
I've got a '68 Roadrunner that I bought in 1987......I built the trans then, I've raced the crap out of it every year and the pan has never been off.........still has the same fluid in it that I put in it back then.......
which shouldn't be very often.........Then it gets a new gasket when I buy an overhaul kit..... 
