I've used Hypoid plain jane cheapo 80w90 gear oil on everything from a 1971 399 Olympique, a 1970 292 TNT. a 1995 P*laris Indy 500, a 1999 P*laris 700 RMK, a 1998 MXZ 670HO as well as several others and never had to touch the chaincases except for oil changes or to pull a track - pistons on the other hand are starting to become a big pain in the wallet.... LOL
I figure if it will last in the rear ends of my brothers Peterbuilt with a 600 CAT - it'll probably be all right in the sleds.
Woodler