Is that engine fan or liquid cooled? either way, they both last forever, but it changes what to look for.
The biggest thing's to look for on that chassis are mainly in the rear suspension, check all the suspension arms and particularly any welds, the can crack under severe use. Also, take a good look at the rear, upper suspension shaft up in the tunnel (the one with the big black plastic wheel on it) it's pretty prone to bending. When that happens, it really binds up the suspension, makes it feel harsh.
Reach up into the front of the tunnel, grab the crosshaft (that drives the track) and try and wiggle it around, any play or clunking is bad. Those bearings go frequently on most sleds. It's a cheap fix, but takes an afternoon to get it all apart to fix.
Look through the fan shroud on the recoil (MAG) side of the engine, see if you can see what condition the fan belt is in. Looks for cracks on the inside edge, or cords hanging out. It's not expensive to change, but it can ruin your day if it snaps out in the middle of nowhere. Look at the cable going to the oil pump (on the outside of the recoil housing on the fan cooled models, in between the carbs on liquid cooled), sometimes they fray and when they snap, no more oil injection pump.
Take a good look at the DSA suspension arms on the front, make sure they're not bend or kinked, if they are, they tend to bend the whole frame, then you've got big problems. The one in the picture might be a bit bent right where the decal ends. Take a look at the radius rods under the front end (from the DSA arms to the center of the chassis), they can get bent on stumps sometimes as well.
Check for oil in the chaincase, make sure it's not milky (full of water) or full of metal shavings on the end of the dipstick (excessive chain wear)
I like to start the engine, and run it quick with the belt guard off and the hood open, (make sure the track is securely supported off the ground!) watch the clutches shift, make sure they shift smoothly, then test the brake.
Take a good look at the track as well, make sure no lugs are missing, an if any are, make sure you can't see the cords underneath them, that can really weaken the track. A few lugs broken off partway is par for the course with a deep track like that ( and nothing to worry about), but torn off down to the cords is bad.
That's my usual checklist, hope it helps! Good luck, it looks like a decent machine from the pictures!
