If you're talking about the lower bearing (cross shaft) in the gearbox, they're the problem ones on just about any sled, they're exposed to snow and ice on one side, and the other side is bathed in gear oil full of tiny steel shavings from the chain and gears. They're double sealed, but eventually the crap works it's way by on both sides. The upper one's (jack shaft) don't wear out as fast, but can still wear out in time. The good news is just about all Ski-doo's use a standard 6205 bearing in the chaincase, same as the bearing in all the wheels in your skid frame, and you can find them for less than $10. It's a little labour intensive to change (pull the rear suspension, take the cover off the chaincase, pull the chain and bottom gear, take the cover off the bearing on the other side located below your secondary clutch, wiggle the shaft out and change the bearings, might as well do both while you're in there, reverse the process to put back together), but can easily be done in an afternoon with some simple tools. Good luck!