I recently purchased a 2001 Aztek it was a great find only 76k, everything over the years has been changed and kept up the only thing is transmission fluid. My transmission fluid is still red the car shifts and runs great I did ask my mechanic and it is "dirty" and he recommends changing it. I know some people say older transmissions have issues after change and what not so should I change it or not ? If so should I have it flushed ? All help is appreciated!