Just to clarify, the head's tapped bolt holes for the intake bolts aren't tapped into oil 'passages', at least anything pressurized with oil. (There is one head bolt that has the rocker oil supply passing up through the head bolt hole.)
The shop doing my valves didnt use enough on 3 of them. Couldnt figure out where the oil was coming from. The hot oil under the valve covers WILL migrate up the threads if not properly sealed. Sneaky stuff, that Mobil 1.