My new-to-me Fat Boy had some white-colored pipe thread sealant on its three oil drain plugs (engine, chain case, transmission). Each plug also had an O-ring. The transmission O-ring was broken and caused the plug to be under-torqued. I'm not sure any of these threads are tapered. If no then pipe thread sealant is inappropriate here. The sealant can get inside the engine's oil passage, block oil flow and result in damage. I think it's better to simply replace the O-ring every time the plug is removed and don't over-torque the plug.