I think what your refering to is a total flush of the fluid.There are 2 basic kinds of flushes the 1 st one is worthless.It pumps out the old fluid while the pan is still left on leaving whatever debris there is floating around in the trans

Theres flush method number 2 where the pan is dropped and then all the old fluid is pumped out and replaced with fresh.This is also the best method but done the least.

As for buying cylinoids I agree if the pan is off and you got $ then replace them while you can saves time later.