I still can't source the oil leak though. There doesn't appear to be a hole or crack in the head after all.
The mystery of the leaky stud is going on the back-burner for now. I'm taking the head to have it heli-coiled tomorrow and ordering new head gaskets in the meantime.
**Update** Mystery oil leak was probably one of the gaskets between the head and mechanical fuel pump or the valve cover gasket most likely.