A GL5-only gear oil is not suitable, but many of the newer gear oils now conform to a newer mil spec qualification that requires better compatibility with copper containing components than the GL4 spec while having better wear resistance than a GL5 gear oil. The specification is MIL-PRF-2105E (aka J2360 after Jan 1, 2004). A good example would be the Amsoil Severe Service gear oil. Its listed at GL5, but it also conforms to MIL-PRF-2105E (aka J2360), so it has excellent compatibility with brass gearbox parts. Not sure how a syncro box would work with an oil like this though.

 

Add a little Lucus Oil Stabilizer to the mix and it gets even better!

 

I hope that was sarcasm. Link

 

We use Redline lightweight shockproof in the trans due to Shep's recommendations from his testing. We use Diaqueen in the t-case and rear diff. We used to use BG synchroshift II and had no issues with it to think of but changed cause Shep builds our customers tranny's.

 

BG might work in well in Alaska, too thin here and made too much heat, for me in my climate MT90 for about 60,000 miles (changed about 6 times) seems to do the trick

 

I just changed from MT-90 to Amsoil MTG. I also put Amsoil SVG in the transfer case and rear diff.

Shift is nice and smooth. I wasn't unhappy with the MT-90 but I like this better.

Oil Doc is great! Thanks Oil Doc

http://bestoil4you.com/Evo.html

 

Redline MTL/MT-90 mix for all my cars and I love it!

 

^^^
2mt and 1 mtl or 2mtl and 1 mt?

 

I have 120k miles and have always used Mitsu Diaqueen. Switched to BG II for 10k miles, and my transmission was pregressively getting notchier. Went back to Diaqueen and it fixed it. Never used anything else since then.

If you race, just change it out more frequently.