I just bought a '99 YZ 400F and was wondering what the "known issues" were for these bikes? I checked out motoman393's website and appreciated the great article about the chain slider and the "cheap" fork tools. I was also reading that us Yamaha guys better go out and grease the head bearings. Are the head bearings a common problem for Yamahas? What other things are known to cause problems for these bikes? I've got a good idea on general maintenance (valve clearance, linkage greasing, oil changes etc.). I just want to know what Yamaha special issues I should be looking for.