Lube manufacturers do a great deal of research and put additives in their products based on facts, not guesswork or "old mechanics' tales". Messing with the hypoid lubricants in rear end grease would be unwise at best, and possibly a disastrous mistake. We used to use straight mineral oil without hypoid additives in Fuller Roadranger transmissions in the big rigs to avoid getting carbon deposits and early failure of synchronizer rings on the air-shifted range selector synchros. I don't think that would be a concern on a stovebolt transmission. Just use the same hypoid lube in the transmission and the rear end.

I've even seen some shade tree wrench jockeys add a couple of handfuls of sawdust to a rear end to try to quiet down gear noises- - - - -that didn't work, either!
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!