Use redline MT-90 tranny fluid. Some members are also using GM synchromesh with good results. Anything is better than the stock fluid. I use Amsoil 10W-40 high performance synthetic with my MSP. I also only drive it in the summer in good weather. If you are going all season you can't go wrong going with the manual recommended 10W-30 (or 5W-30 for colder weather) synthetic from Amsoil. Do a search, there is an Amsoil dealer on these forums and plenty of threads on people running different oils.