My thoughts were with txrider's, but if you haven't repacked the head bearings, don't worry about them.
First off- smell it. Seriously. Different oils smell differently, and they have different 'slickness'. You might get a clue on it from that.
Secondly, clean it off and keep an eye on it- you might be able to backtrack it to the source (the big banjo is sounding pretty good to me now). Oh- on that banjo fitting- check to see that the vent tube is still attached. One time, when I removed my starter, I managed to pinch the vent tube and then I subsequently blew it off at the top fitting. I didn't blow oil, but I could see it happening.