I have a Bombardier 1962 SW54 that I need to change the differential oil. The Operator's manual that I have states "replace with 4 gallons (31/2 gals. for SW-48) of non-corrosive, non-hypoid gear oil, SAE 90 or SAE 80, according to prevailing temperature". Obviously major advances have been made in lubrication since 1962 - what oil would be best to use for this application? I've been told that you need to be careful of the type of oil because the brakes are also submerged in the differential bath and some newer oils will affect their performance - while I would obviously want to use newer more effective oils, I certainly do not want to adversely affect any of my components!