Agreed, the lube can cause problems, but I'd be a little spooky about using the 50 weight motor oil. Find a diesel shop or truck stop where they service Fuller Roadranger transmissions, and buy a quantity of "mineral oil" that they use in the Roadranger trannys. it's 85W-140 weight, just like the hypoid lube, but without the super-slippery additives. Hypoid grease in a fuller transmission causes heavy carbon deposits on the synchronizer rings.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!