First off im new here so hello to everybody, second a friend of mine has a 2000 400 ex that i am thinking about getting, and it was smoking really bad so we tore it down and the cylinder looked fine but the exhaust valv:huh:e had about a 1/8 inch of something that looked like carbon buildup but was white on it, could this be from burning oil , do u think it needs valve seats or seals or maybe just a set of rings, it runs fine just smokes and uses about a quart of oil in 8 hrs, thanks guys