My 03WRX just hit 11K and want to change my 5MT fluid. I wanted to get some input on what any of you have used and would recommend/not recommend for improving the performance of our fragile transmission.

The car is mostly for daily commuting with the occasional autox.

 

Just put in dino fluid, any choice is a good one most of the time. Stay away from the gymick ones but besides that choose a good company to run oil and then get some GM Syncromesh and put a quart of that in.

A lot of guys have put in synthetic tranny fluid and it feels great for the first week then the syncros start going down hill. The fluid is too slippery for the syncros to slow down the gears and catch so it just wears them down triple speed.

But synthetic in your differentials is ok (if you were wondering)

Good Luck
WRX Rush

 

From what I've been reading in the threads, a majority of people use Redline 75w90ns or Royal Purple. Anyone have any issues while using these oils?

 

So going back to the STOCK/OEM subaru tranny oil is best????

 

With the addition of 1.0 - 1.5 quarts of GM syncromesh. It makes it feel like a brand new tranny.

WRX Rush

 

same here. GM syncromesh works great.

 

I've been running royal purple 75-90 synthetic for the past two years and I havent had a problem.

 

Everyone who has used GM syncromesh seems to like it. I have not used it yet. I have however used Motul gear 300 and Mobil SHC (hard to get) both work exceptionaly well.

 

Gear oil information here:
https://www.i-club.com/forums/suby-shopping-maintenance-warranty-92/what-fluids-use-your-subaru-46582/