I use royal purple. It's somewhat expensive but how often do you really change your tranny oil. I noticed my car shifts smooth and a slight increase in milage. This is from experience w/ my 240, make sure you have the right size gear oil pump and that you can remove the fill plug before you pull the drain plug. On the 240 you can remove the shifter and pour the oil in from there. Don't spill any, it smells horrible.