I had the same issue. had to tear things down to removing the lower intake (what fun) and that cap, it is a pain to clean between surfaces, once I got what I could with Q-tips (par Doerr's advice) I just soaked a string in solvent and flossed around best I could, squirted some sealer in there, rotated the cap to work it around, and well, THAT oil leak stopped.
If you ever have the heads off the engine, go ahead and do it the proper way but yeah the head is right in the way of it moving more than a fraction of an inch.
