found my metal in oil problem in my 450. The primary drive gear nut backed totally off despite having a lockwasher. the washer was split. also found a a loose circlip. the end of the crank is slightly scored but otherwise the threads are ok. Looking at the manual the crank goes to what looks like a boss that goes to the oil filter cavity. Is there a seal in that boss? My cover is a bit chewed up and I'm not sure if I'm missing something else there. Not sure why this would happen considering a lockwasher. Any thoughts?