This seems to be one of those topics that provokes endless controversy. But I have yet to see evidence against doing this. Not really a flush but a fluid exchange. Open the cooler return line and let the old fluid pump out while re-filling at the dipstick. No solvent introduced. I know on older cars this was a no-brainer but what about the newer electronically controlled units? I have a friend that did an engine/transmission swap without checking the filter as he *ss-u-med it was fine. YUK! Totally filthy. It is a Camaro LT-1 engine into a Malibu but I don't know what trans it is- something from the late 90's. I advised him to do the fluid exchange and he posted it on a Chevy site somewhere and got immediately flamed for even thinking about doing that. What is the harm?