I am overhauling my 1996 Camry and as part of that overhaul, I decided to drain the transmission fluid and replace the filter. The car has 131k miles on it, and I bought it new so I do not know whether the fluid has ever been changed or not. Now, I just read a post somewhere else that said if the fluid has been in the vehicle for 80k+ miles, it would be best NOT to change it because the grit in the old fluid is not acting like liquid sandpaper, giving the transmission extra "grip". They said that replacing the fluid with clean fluid could actually cause more harm than good. Did I just make a big mistake? :banghead:

No, I doubt it. You didn't change all the fluid, just 2 quarts out of 6 total. There is a lot of fluid trapped in the torque converter and the valve body.

I would periodically drain and fill the transmission (maybe every 5-10 k miles) to slowly bring the fluid back to a decent state.

Don't forget to change the differential fluid also. It is filled with ATF.

Harm?? I doubt it. I replace mine every 75k or so on my 95 camry and it has 239K on it with no problems. It would do more harm to never replace it. I just roll mine up on ramps and drain the pan, fill it back up, drive it for a mile or two and do it all over again until it is a nice bright red again. It will take a few gallons this way but it has worked for me. My Tundra now, it takes a little more than a few gallons!!!