GL5 75W90 is the Subaru recommended spec for the gearbox and rear diff.

Redline Shockproof sounds good from what people say but I am trying to see which type... unless anyone has a better suggestion? Castrol Syntrax? Any preferences?

However for 75W90:http://www.mtmotorsport.co.uk/redlin...ear%20Oils.htm
"Not suitable for synchromesh gearbox use, as the extreme slipperiness can cause gear clash"

So do I go for 75W90NS? Neither of these are "Shockproof" though.

[Edited by john banks - 10/13/2002 9:44:48 PM]

When in doubt, just go for Syntrax as its what 90% of us use here anyway. I on the other hand tried Carlube Hypoid recently and have not noticed any difference (I like experimenting).

Syntrax is def the stuff to use. Ive tried a couple of different fully synthetic oils, which claim big things. They did not impress in a subaru box.
Tried Castrol TAS fully synthetic GLI-5
Tried Castrol SMX-S fully synth, for supposedly notchy boxes ( known as Castrol Syn-torq in the US apparently, and what is recommended for Vipers. )
Syntrax was much better. Another good oil is Castrol SMX

I have also tried various oils in a Toyota Supra turbo box, which although is different, may still have some relevance.
I tried both Redline MTL-90, and HD Shockproof, of which the shockproof was better. Both were quite notchy though.
I recently tried Syntrax in the box, and the difference is quite impressive. Gearchange is much better, and feels like it should be.

we use either castrol syntrax 75/90 or Prodrive told us to run Mobil 75/90 synthetic in the rally car thats if you can get it without a bank loan.

JOHN, i used redline hishock. It comes in three weights of which I used the heaviest but arguably it is no more viscous than the standard recommendation for our boxes, just much higher tech.

It made the box lovely to use, like aknife through butter. I bought it from demon.

I agree 100% about the Syntrax for the front diff/gearbox but go for a different oil type in the rear as it's completely different case (lower temp, other diff type/wear etc).
JIM