I needed a new clutch in my 09 YZ450. Ordered up the parts and took it apart and the boss and the pressure plate were badly worn with groves dug in as were the outside of the 1st and last friction plate. This can not be normal. Has this been a problem for these bikes? Where does this come from? Left over machining bits from assembly at the factory? Never had any jurkiness or problems with the smooveness of engaging and releaseing the clutch. For background I have had 2 other 400/426s since 99. Never put a clutch in any of those. The 99 in particular was abused much more than my new bike. Has durability of these bikes decreased over the years as they have gotten lighter and more powerful? I do notice that people are recommending a lot more piston, ring and valve train service on these bikes than I have ever done in the past.