I have a 96 OBS with about 90K on it. About a year and a half ago I changed the tranny fluid to Mobil 1 GL-5. From the beginning I noticed that the synchro on second gear was not working as well particularly under a hard load. However, I never guessed that the gear oil could cause the synchros to work less well. Then yesterday I stumbled across Cobb Tuning's technical article on gear oil and decided to try Redline MT90. The difference is amazing. The second gear synchro works perfectly even if I really stomp it and shift fast. I have read all the threads about gear oil and the fact that MT-90 is GL-4 rather than GL-5. However, is there anyone out there that has really had long term problem as a result of using MT-90?

 

Thanks for the message. The difference in shifting and synchro performance is so dramatic with MT-90 that I am going to continue to run it. I have looked at all the transmission threads and wonder if Subaru's recommendation og GL-5 in its transaxles isn't at least partly to blame for all the synchro complaints.