An o-ring - never thought of that for the oil pan. I picked up a filter today from Honda, and cleaned all around - turns out the shift seal is leaking, that, and I suspect my petcock is contributing to the problem. :-( Seems to be a "sour-spot" where the petcock lever doesn't seal quite right.
The Honda parts guy thought I had to use "special" motorcycle 10W40 oil for this - I hadn't realized there was - or can I use "regular" auto-zone 10W40 that I'd normally put in a car?
Thanks,
Dan
'71 CB500