I'm about ready to change the manual transmission fluid on my 02.
I've heard many arguments about not using synthetic fluid in the tranny.
Anyone have any thoughts about this, and has any used synthetic fluid and had any problems. The dealer said there shouldn't be a problem using syntehtic fluid in the tranny but not in the rear diff.

 

i Stick with the OEM stuff and havent had any problems at all with it. i remember someone posting up that they used redline synthetic tranny fluid in their STi and had to get it rebuilt cause the synchros went out.

Just stick with OEM and there shouldnt be a problem.

 

On my 60,000 service the dealer put synthetic in without my knowledge. Shifts were rough, felt like it does first thing on a cold day before oil warms up, only it never got better. A couple of grinds, and excess noise. I swapped it out with the syncromesh cocktail (1 qt. GM synchromesh, 2.7 qts. valvoline 75w90 gear oil) after reading tons of posts on it. Shifting feels good now, but doesn't seem like a huge improvement over OEM. Still, I'll probably continue to use the GM synchro stuff from now on in hopes of preserving life of my synchros.

 

Has anyone had good luck with this kind of cocktail? Is using the GM syncro mesh stuff a good idea? Seems like using the oem 75-90 stuff seems the way to go

 

If you are not having any specific problems with the transmission at this point, it's probably best to use non-synthetic 75W90 GL-5, or 80W90 if you can't find the 75.
You could also just leave the transmission fluid alone as long as it appears clean and full and there are no transmission issues. Subaru does not actually specify a service interval for the transmission oil, it's just something that people commonly do at the 30K service.

 

Many people seem to favor the cocktail approach as seen by the number of posts on here about it. But people on here do a lot of weird things...

Looking back at the first post, you mentioned the dealer said synthetic was fine in the tranny, just not in the diff. I think I have read just the opposite on here. Either way, makes me wonder what the dealer put in my diff.

 

any subaru mechanics out there suggest to just leave the tranny fluid alone if your not having any problems? I've not heard that one. I'm thinking about using the OEM "regular"
tranny fluid, there seems to be to many plus and minus by using something other than OEM fluids.