I developed a problem with my 03 YZ450f this weekend, Its leaking water into the oil and blowing oil and water,prolly out of the valve cover breather. Ibelieve the problem to be a blown head gasket and hopefully no more. Here is the question.... I was planning a rebuild this winter now maybe sooner. Im thinking to replace valves with stainless valves and have the valve seats cut, repalce timing chain and tension slider and replace the piston. Does this sound like enough of a rebuild? I have only owned this bike for a year and Im unsure of its exact history. Im sure the last owner didnt get into the motor. Im just looking for advice on what all needs to be covered to make the bike solid and reliable. Its been great until now. I have shimmed the valves once and the middle is using a .180 shim to get it into middle spec. Your thoughts?