While it isn't unheard of for a head gasket to leak oil, it is extremely rare. On our engines, I believe the pressurized oil isn't fed on the outside of the block, those are only return holes. For non pressurized oil to be escaping, there would have to be a massive hole in the gasket in just the right area. I'd follow the advice of other posters and replace the valve cover gasket set. Since they're the highest leak point on the motor, gravity causes them to coat just about everything.