ahh let the dirt pile on. if you keep the airfilter clean oil filled and the tires pumped it'll last a long long time. I'd love to see a build log for this as i'm wanting a big bear irs super badly.
if you'll sell it I'd think very seriously about a cheap cylinder and piston from ebay. but since they are under 100 bucks it does make you wonder if they are ok to use!
I'd say it comes down to your usage case. if you are going to use it weekly and run it like a sport quad then might as well spend up and get some nice oem or name brand parts because it sounds like you got a great deal on it. im actually jealous!