Any Hypoid Tranny/Gear Oil will errode the Brass Synchros that is why it is important to stay away for such lubricants.

I use the MT90 as I do not drive the car in winter. The MTL is a "Lighter viscosity Manual Transmission" Fluid so prefered for years around.

I prefer to put the RedLine Heavy Shockproof in the XCase and Rear End.

GM Synchromesh, Royal Purpule or AMSOIL also have excellent products.

Hope this helps.

Ghislain.