Definitely change the chain case oil each year.
Fuel....did ya' put in stabilizer last fall? If not, then drain it out and replace with fresh.
Also:
- grease all suspension (front & rear) points
- check track clips (look for rusted/broken/missing)
- check carbides and ski bottoms
- charge battery
- check coolant level.
- new plugs (when was the last time they were changed?)
- check belt (look for cracks or missing chunks)
- inspect all wheel bearings...make sure they spin freely.
- do a thorough visual inspection for any missing/loose nuts or bolts.
- be sure to sit on the sled with your helmet on and make lots of "zoom...zoom" noises...preferably with the garage door up, so the neighbors can see 'ya!