I have a 99 yzf400 that I bought in 2002. It is my first 4-stroke dirt bike. I've put over 125 hours on it, and have never replaced the top end, including the valves and springs. I've had the valves adjusted once. I need to know what parts need to be replaced in addition to the piston, valves, springs, and gaskets; like valve guides, cam chain. Also, what I need to look for and ask about when finding someone to do the work. Should they do a leakdown or compression check? Or a solvent test to check for leaking at the valves seat? Should they do this before dissassembly? Are they supposed to check the tolerances and specs of the parts connected with the top-end, like cam lobes, bores, etc., as part of the rebuild? Should they give me the replaced parts? Any ideas on the labor charge?