Is a transmission flush a good idea?

Currently I'm going thru the transmission loop of what's wrong with my transmission and how/where to fix it. I just got off the phone yesterday with a decent independent mechanic shop near me and he discussed this very same question / answer. Basically it goes like this... if you never had the fluid changed, it could be dirty enough to have particles in it which accumulated and created a sludge which stuck to some of the seals/gaskets which may be helping it from leaking. If you change out the fluid, that sludge goes out and now the seals are no longer protected by the sludge and it now "could" leak. In this case, it probably was better not to change it and have the seals replaced. On the other hand, if the fluid was changed fairly often or doesn't appear dirty, it should be fine to change it with no consequences. Therefore it really depends and as he said, it's a crap shoot. He told me that he had one case where he flushed out some transmission and while the car drove in, after the flush it was undriveable (feel sorry for that person).

Depends on how often you've been changing the transmission fluid. Is it red in color or brown? In my view, if you plan on keeping the car, it's nice to have all the fliuid changed, then after that just maintain regular transmission servicing by draining fluid from the pan. If your existing fluid is already in good condition, you wouldn't need this service, but bear in mind, most transmission failures seem to result from "burned" fluid. Once the fluid is overheated, it tends to degrade more rapidly, so changing it often really helps extend transmission life.