I am thinking of buying a 2000 200 exc. The bike runs great after a tranny oil change but after 20 minutes starts to run lousy and the tranny oil turns black. I'm thinking crank seal which is not big deal. But I'm also worried that the crank bearings are going out and causing the seal to leak. The bike does have a few hours on it. Any thoughts? Also, what is the approximate price of crank rebuild if I took the bare bottom end to a shop?