I have in the past been able to supply "O" ring kits to cure the cover leak on the 500/550 oil pump.
Unfortunately my old supplier has changed hands and no longer stocks the "Slow Moving" parts and is not willing to order in quantities i can afford to buy to sell over 5 years!
However to help all out I have been doing some research and discovered that whilst Honda do not list the cover "O" ring as a separate part for the 500/550 the correct size is used on other bikes and so for those in need here are the part numbers and sizes:-
91305-426-003 oil pump cover 46x2
91302-377-000 suction and feed 15x2.5
91302-250-010 casing to block 47x3
Best wishes to all and hope that that helps
