I have an old vintage 1973 Sno*Jet SST 440 that I've recently restored, and I used straight Lucas Oil Stabilizer in the chaincase. There isn't much of anything sealing it other than a couple flimsy rubber seals that had definitely seen better days. At first, I ran 80w90 and it leaked out within a few hundred miles. With the Lucas glop in there, it stays put. The sled isn't a race machine or anything, so thick goop in there is fine. It'll still go 70+ MPH on hard pack! It's not a "daily driver", but still fun to play with on the local trails. I've gotten quite a few thumbs up from other riders, and impressed the socks off a couple when I carried the skis from a dead stop for about 50 feet or so! 38 HP doesn't sound like much, but on a machine that only weighs 300#, it's pretty impressive HP/weight ratio!