ATF replacement

[operagost]

ATF is supposed to be replaced at 100K. As most of us who has ever opened the hood know, the system is sealed. I was going to have the dealer replace it at about 150K-- yes, I forgot-- and he suggested leaving it alone until the trans needed a rebuild, as the fluid was think and he thought I might have more trouble with new stuff in a worn trans. The trans works OK under normal circumstances, but it does shift late when at or near WOT and, sometimes if I punch the throttle when the car is rolling, it shudders (it's only done this twice in the past two years). Reverse works perfectly. So should I just leave it alone until I have problems under normal driving, or change out that fluid and see if it really needs a rebuild? I don't have any real plans to replace it, and I do have a backup vehicle.