The reason the woodruff keys are breaking on the 03 WR450's is because the idler gears are constantly engaged to the flywheel and starter. They are not designed to spin backwards. So, when a kick back occurs, the flywheel can't turn backwards so the woodruff key snaps. Yamaha of Japan has a new design for the idler gears that allow them to slip at a lower torque so that during a kickback condition the flywheel will not be mechanically locked on the starter. Yamaha USA either does not know about it, or they are playing dumb. Check out the posts at http://lists.off-road.com/mailman/listinfo/wr450 for proof.