Ever since I had my heads rebuilt (by Bob Grauer, SF Cali), I have not had a problem with oil leaking at the valve cover. I don't know how long it has been. He MUST have trued them up, even though he did not mention doing it in his labor charges...
I am very happy with my OEM valve cover gaskets, now. Before I had two gaskets on the left side. That is a sometimes successful fix.
I don't know how much my sump is leaking, if at all, but the bottom of my engine is a mess. I couldn't imagine getting it clean without pulling the engine. I replaced my push rod tube seals when I had my heads rebuilt last fall.