Leak down test won't show it as the leak is upstream of the valves. It tends to leak right along the lower edge of the intake gasket. I actually had a gouge in my intake along one of the edges that was agravating the situation. In addition, when running, you've got a vacum inside the intake runner that also "sucks"
oil through any gap. Haven't figured out any way to test for this and just tried to be liberal with gasket sealer - particularly along the bottom edge of each of the intake openings in the head. Cornering hard also can aggravate it when you get
oil sloshing up to one side. You might try to see if you're getting smoke upon hard cornering.
Oh, and the other issue - this might now be the issue! Mysteries of the 427 are never ending sometimes
