Well... it depends on if you just want to be anal about it or not:
Non-Anus Checkup
- treat the bearings as if they were shot. Plan to replace them. TS is offering a new bearing update kit for $150 that is hilariously cheap compared to buying all the parts after the offer. You get a new driveshaft, bearings, and bearing housings. You'll need to have the old drivers pressed off and onto the new shaft.
- ride it
Anus Checkup
- see bearing update above. absolutely do it unless you like leaving your bike in the woods overnight
- check the welds in the kit up front where it attaches to the bike. shine a flashlight up in the joints to make sure there are no cracks. there was an issue with some 2012 bikes (mine was one of them) where these welds broke in the woods
- check the welds on the rear suspension arm to the upper shaft for corrosion
- make sure there is some life on the idler wheel in the chaincase. Over time the idler wheel gets beat up and you lose chain adjustment
There might be some other things that are good to check, but these the main areas I think you should look over before you put money in hand. Keep in mind that in 2012 some of the things you won't get that were updates done to 2014 are:
- 10 inch wide ski with dual runner carbide
- front flex arm
- custom molded Camoplast track for the Horse
- new rails
- heavier rear suspension spring along with suspension update
Of all those things probably the one that is the most important, if I had to chose one, was the ski upgrade. If you don't get the new ski you'll want to buy an upgrade from TS. All things to consider on the asking price.