What kind of riding do you do? The YZ450s of that era produce a TON of heat, and have small oil capacity/radiators. If you do a lot of trail plonking, they still build up quite a bit of heat. Check your oil often and make sure you allow it kind of "air out" from time to time. They don't like sitting idling.
"Living just to keep going, goin' just to be sane." - The Black Keys
I prefer kick starters, air-cooling, and carburetors over anything.