I have an antique snow blower i'm restoring. I pulled apart the differential and replaced several components. It says in the manual (from 1973) to use mp-90 gear lube. what is the equivalent. I was thinking of dropping in some 85w-140 or 85W-90 gear lube. When taking apart the gear box it's pretty much a cast iron box with a couple of gears, a bronze sleeve bearing and some needle bearings.