I have a identical problem as another member, flywheel came loose, broken woodruff key, shaft nut came off. I owed engine since new without prior work. I had a certified tech replace trashed stator, new key without new flywheel. He torqed nut down. Within ten minutes in water the nut was loose and key broken again. He says its not the flywheel but some mistory harmonic vibration. Does anyone have any idears?? Thanks