Gear oil is a topic right behind engine oil. Yes the Amsoil is a wonderful product. So is the Redline. However the myths around needing GL-4 is not quite right especially since modern gear lubes don't have the corrosive characteristics and damaging the brass synchronizers is not a real issue. As for the next concern of the better fluids not having the right friction characteristics for the synchronizers to work properly that is also a bit of a myth and you really can't speed shift or get anywhere fast in a vanagon anyway. 

Synchronizers are cheap. The part that needs maximum protection is the ring and pinion set. For that you want the GL-5 or better lubricant. Viscosity is also an issue and like the engine for high speed travel the gear box is also thermally challenged.  Amsoil and a few other offer a 75-w110. About 3 years ago I began using 75w-140 and even in winter I find very little difference in cold shifting ability. So that is what I am no recommending. Cooling and viscosity is now recognized enough that Weddle and GTA offer fittings on the transmission so a pump, cooler and filter can be added. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Jack R
Sent: Friday, June 5, 2020 8:19 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Amsoil GL-4 75W90

Has anyone used Amsoil Gear oil in their Vanagon Manually Trans?

https://nam03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.amsoil.com%2Fp%2F75w-90-long-life-synthetic-gear-lube-fgr%2F%3Fcode%3DFGRQ&data=02%7C01%7C%7C392ef5cde2314cc144b208d809af2fd1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637269995308448401&sdata=oFsco%2BBfo4NDBzaSGew0i2sjFkf3a0UlUwdF9s12ntc%3D&reserved=0
T-EA#pills-home_0

I worked for Meritor for 9+ years, and our engineers said that Amsoil performs exceptionally well.

Currently running RedLine GL-4, for the past 10 years, only 20k miles on my rebuilt 4-speed.

Jack R.

84 Westy