Leaking from head bolts

I've seen 318s from all years from the 1970s onward with blind head bolts and wet head bolt holes. Most have been open in the deck towards the valley but some have been open on the exhaust side of the head. I think it was more which plant they were being cast at and when more than it was a corporate wide policy on iron reduction. I have noticed it is always in higher dash numbers (coring mold revision) blocks than in lower numbers. Most have been -12 and higher.