You seem to know these bike pretty well. Went for a "spirited" ride on Saturday on my newly purchased '75 550F (8300 miles) When I got back there was some (not a ton, but maybe a 1/4 cup's worth) of motor oil dripping off the chain and chain guard...plus there was some on the rear wheel (evidence it was spraying out during the ride). What is causing this? Is there some gasket behind the chain guard I need to replace? Any advice is appreciated!