Redline MTL has a bad habit of eating thee plastic bearing cages in the older transmissions, I've replaced quite a few mainshaft and countershaft bearings years ago.
BTW, I'm Transzex on D-Series.org, also know as Mista Bone on Honda Tech and other sites.
Most of the street LSD transmissions I've built, the owners are running Pennzoil Synchromesh without issues. I know Matt Downing is using it in his ITA car, but I don't think it would stand up to the heat of an enduro car. It is 5w30 base viscosity.