What gear oil do you prefer for your Subaru gearbox?

I bought an old Outback with a 5-speed manual and I'm in the process of changing all of the fluids, filters, and wear items.

A decade or more ago I used Redline Lightweight Shock proof gear oil in my '97 Impreza and my wife's '93 Impreza and I noticed a reduction in the crunchiness of the synchronizers, particularly in my Impreza since I hadn't been very nice to that gearbox.

Is there any particular oil those who abuse their Subarus swear by? I'm out of the loop. It shifts fine now, aside from the worn out bushings, I'm just changing it since it's likely never been changed.

Shockproof is nice but it wears out very quickly.  About 2000-3000 miles.  After that, all of the calcium (I think) chunks in it that provide the "shock proofing" are ground to dust and it is just expensive funny colored gear oil.

I have never gone wrong with whatever Coastal fluid I can buy in gallon jugs for $20 or so.  Fresh fluid is better than old fluid, mainly.

I'm using Redline in mine and it's worked well for the last several years.

Nasioc forums had a magic concoction for 5 speeds, a mix of a few things and sacrificing a small animal at full moon.

That was "Scotty's Cocktail" I believe. Might give that a google. 

Here you go, I haven't tried it, so I'd approach this with the same skepticism you'd approach anything else on the internet: 

2qt 80w90 Castrol HypoyC(NOW labeled Axle Limited Slip 80W-90 by Castrol in North America) NO stupid PM's on this either 

1qt Redline HEAVYWEIGHT SHOCKPROOF....NOT the LIGHTWEIGHT!!!

1qt Penzoil 'SYNCHROMESH' transmission fluid....the GM synchromesh fluid PN 12345349 is available at any GM dealer and can be used if the Penzoil product is not available....the Penzoil one IS better.
__________________________________________________ _________

1) FOR BEST RESULTS DRAIN THE TRANSMISSION FOR AT LEAST 30 MINUTES...REMOVE the trans dipstick and use a funnel(see below) with a long spout....

Pour the WHOLE BOTTLE of the HEAVYWEIGHT SHOCKPROOF(NOT THE LIGHTWEIGHT) into the trans....

2) Pour EXACTLY  1/2 of ONE of the bottles of CASTROL into the now empty shockproof bottle and shake it gently.....and pour THAT into the trans

3) Pour ALL REMAINING CASTROL PRODUCT into the trans.

4) Pour EXACTLY  1/3 of the 'synchromesh' into the trans and replace the dipstick

5) Drive car in a NORMAL AND RATIONAL AND REASONAL MANNER using ALL the gears INCLUDING REVERSE.....

6) Park car on LEVEL surface....wait at least 20 minutes and check trans fluid level.....top up with the synchromesh product.

THE 5MT TRANSMISSION DOES NOT LIKE TO BE AT ALL UNDER FILLED....A BIT OVER FILLED IS BETTER THAN ANY UNDERFILL AMOUNT.
OVERFILLING THE TRANSMISSION S L I G H T L Y IS NO BIG DEAL.....DO NOT WORRY ABOUT IT.  NO stuid pm's or posts on this please

A

The same guy would also berate you if you wanted to know what your spark plug gap should be, because he was the only person in the world who knew how to gap a plug.

I'd just use "whatever".  Fresh is better than old.  99% of the time, that is the difference that people feel when they change gear oils.

When I feel fancy, I will run a small amount of ATF (Type F if available, Dex III if not) for the friction modifiers.   Type F is "grippier" than Dex III.   How much do I use?  Well....  the gear oil comes in gallon jugs, I have kind of a forever-stew pot of gear oil that I combine partial containers into, it is more like cooking than chemistry, so let's say ratio is 2:1 to 3:1.

Thanks

Pete. (l33t FS) said:

The same guy would also berate you if you wanted to know what your spark plug gap should be, because he was the only person in the world who knew how to gap a plug.

Yeah, the way  Scottie's "recipe" is written up reads a bit internet crackpot, so I'm not surprised to hear that he also holds some eccentric views about plug gaps. 

I suppose in a transmission you've got conflicting requirements in the sense that the synchros need a degree of friction to work, but you want to minimize friction on the bearings and whatnot. Stick a diff in the same box with all the shearing action of hypoid gears and it's even more of challenge.  
I like the idea of mixing some ATF in with the gear oil. Had a couple of non-Subaru cars which called for ATF in their manual transmissions and they seemed to work and last well enough....

Isn't Subaru picky about needing GL4 and not to run GL5, or am I thinkng of another brand?

To bad you aren't closer, I think I have 2 -3 unopened quarts of Redline MTL that never got installed in my sons SX4. 

I've had various MT Subarus over the past 15 or so years.  So I've tried all sorts of Smurfblood concoctions dreamed up by internet experts.

The local Subaru indy shop I've been going to to grab fluids lately recommended Motul Gear 300.  And I swear, it's the first thing that ever felt "better" inside the gearbox.

Every Miata or Nissan I've had responded great to Redline, but the Subaru boxes seemed immune.

I wound up using some synthetic 75/90 in the gearbox and rear diff. 

Oh God... Uncle Scotty's Cocktail. 

I ran that in my 2002 WRX before I knew better, and it worked, sorta. I swapped it out shortly after once things started getting grindy with Redline Lightweight Shockproof. I ran that for years with no issues. One thing to avoid is Mobil 1 gear oils in Subarus. Not sure if this is the case anymore, but the friction modifiers in the oil didn't play nice with the synchros and other internal parts.