I just bought a new yfz450 and the service guys told me NOT to put on a K&N filter. They said that the K&Ns allow small grit to get past which will grind off the coating on the valves and eventually cause them to fail. Supposedly they have just serviced a bike that had this problem. It sounded a bit crazy and I love K&Ns but I don't want to blow up a new motor. Any experience on this subject?