I have approximatley 5000 miles of aggressive tight trail riding on my 400. Only trouble I've had (besides normal wear and tear)is a cracked throttle valve, (Just the flat part) which caused a very high idle. It must have been a defect. I'm now hearing some knocking or slapping noise inside the motor. I will rebuild the engine this winter....Rings, piston, timing chain, and check the rod etc.. Is there anything else that has given big troubles that I need to be aware of that should also be replaced while I have it down? Maybe the water pump or\and the oil pump? Also is there any place more reasonable on prices? I paid 70 plus dollars for that throttle valve that had about .03 cents worth of material in it, about the size of a half dollar.