Tha top two if they had good compression and crank seals would run forever. Just clean the carbs every year like any two stroke or your asking for trouble. As for the third one it would run really fast for a while........ Things I always check on a used sled comp., seals, track, rear skid, if those all check out there's not much that can go wrong that 100 bucks a few beers and an evening in the garage with the shop manual can't fix ( same does not apply for newer sleds).......I'm jaded if you have a quad you can only get to where someone else has gone before I wouldn't want to be breaking trail. That's not what ice fishing is about for me I like the solitude.