Originally Posted by My0gr81
Caution: If you already have high mileage on your existing transmission without having done any fluid change, you will be bettter off leaving well enough alone. New fluid would probably cause more problem as it's new found detergen capability may dislodge contaminants into the system.
Fresh transmission fluid will dissolve most gunk that builds up and your filter should catch it. You need fresh fluid to keep your o-rings and seals swollen. If you haven't changed your fluid in a long time I would highly recommend you do so. The transmission may slip at first because now the fluid is able to get around your seals but eventually they will swell back up again. I would also recommend a filter change if it is over 100K since you last changed it. I believe Lexus claims lifetime fluid is good for 100K. My dealer recommended 60K. Canada is 50K.