In my search for the perfect fluid for both the tranny and rear diff of my 08 STI I've come across what some seem to think is the bees knees when it comes to Subie trannies - Go Extra S 75W-90. If you do a quick search you'll find that it's only available in 20L (~5gal) buckets. The quarts can be found, but at a premium paid to those few who have transferred this wonderful fluid from said buckets.

My questions are: who makes it; have any of you tried it; and is any GL-5 gear oil really better than another? I want to do what's best, but I'm thinking the mysterious and hard-to-get factor with this oil may lead some to "feel" improvements after a change when none exist - at least no improvement that couldn't be had by any other gear oil of the same spec.

Thanks for your input!

Motul 300 Gear
Amsoil Severe Gear
Red Line 75w90NS

You could not go wrong with any of these proven products. Dump the rear gear oil asap to get rid of the large metal shreds.

Why the NS over the regular RL? Motul is good, but it's almost $20/liter! I'm going to see how much my local part guy has Amsoil for. He also has Royal Purple, but I'm less inclined to go with it, although not for any good reason.

Here is a 31 page thread about this oil:
http://www.legacygt.com/forums/showthread.php?t=62614&highlight=extra+oil

$12/qt at fredbeansparts. Expensive, but not outrageous.

+1 minus the RedLine suggestion. While it appears to be the perfect fluid on paper it seems some at subaruforester.org have had poor experiences with it. That being said, I have no personal experience with it and can't back up what has been said at SF.org. It has the right specs so it couldn't hurt to give it a try.

I use Motul Gear 300 with great success in manual tranny and rear diff and I'll be sticking with it going forward, even at $20/quart. I don't want to experiment now that I found something that works.

Extra S appears to be made specifically for Fuji Heavy Industries and seems to have the right friction modifiers for nice synchro engagement in the fussy 5mt from subaru. Again, no experience with it personally.

Amsoil is also a favorite on my local subaru club forum at http://www.ottawasubaru.com/forum/. Very experienced and long time subie owners like to mix it with a Redline's MT90 to get the right balance of friction modifiers. However, I wouldn't recommend putting any GL4 rated fluid in the 5mt due to the hypoid front diff. GL-5 is recommend for a reason, even if the synchros don't seem to like most GL-5 fluids.

Well, I confirmed with the dealer that my tranny fluid was changed out while they were looking for a tranny-related rattle earlier this year. Apparently, FHI decided to change the baulk rings from copper to carbon. The effect is better shifting with the downside being a loud, balls-in-a-can-type sound when cold. The tranny pan was dropped before the TSB stating such came out.

It looks like I'll just be searching for a good gear lube for the rear diff now. I need to look into how much shipping will be, but I'm inclined to go with Motul. The local dealer has Amsoil Severe Gear for a little less than $15 here, though...So many choices

It would be cheaper if I could get in on a group buy, but as is, with shipping, it's $18.59/qt. Shipped, the 5gal pail is $192 - that's $9.60/qt. I'm inclined to believe every one when they say the Extra S is great in the tranny, but when it comes to the rear diff I have to believe there are better options for ~$18.59; specifically, Motul 300 or Amsoil...

gathermewool,

In cold NH Winters Subaru Gear Lube does not cut it, shifting is laborious until the car warms up. I switched to Amsoil Gear Lube & I did not have the cold shifting issues.

Regards,
~Button