Buying a 2520 XL 2006. Yamaha 250 has 190 compression in all cylinders accept for two which have 125 and 150. Any advice? Dealer is going to try running a decarb through it and see if it clears up. If it does not clear up how much money should be knocked off the asking price in the event it blows up a few years down the road? 10k? or run?