I had that on mine as well. Tasted it and found it WAS jizz... Just kidding.
I thought I had a bad head gasket, but my problems were more to do with a bad valve cover gasket, leaking oil into the plugs, as well as a bad radiator. I was under the assumption that the oil cap gunk had something to do with it, but not really. I'd say clean it out and let it be. Worst case, change the oil, change problem parts, see if it goes away.
The brown stuff is from Olestra chips, they cause leakage. But not from the car.