Hello everyone. I just bought Fatboy 114 115th anniversary edition. After riding it for a few days a rattling sound started coming from the primary cover. After opening the outer primary cover I found a plastic nut/retainer about 2inchs in diameter laying. No idea where that came from. After removing that bike was alright no sound at all. Infact the gear changing got smoother. Can any one tell me what that black plastic nut is for. I have watched serveral videos of removing primary cover but that nut was not there. Help plz