My guess is that your intake was not sitting square/flat and it was allowing
oil to be sucked in. A .020" gap is a mile.
My SOP for intake gaskets is Dow Corning 732 in a caulk gun tube. I've been using it for over a year now and have fallen in love with it. On engines that are not going to see disassembly anytime soon, I will run a small bead around ALL ports, including air/water. I will then set the gaskets down and lay the intake down on the gaskets for a few hours. After I'm sure the gaskets are nice and glued down, I will pull the intake back off and lay another small bead around ALL ports, then lay my beads on the china walls. Dow Corning 732 is FE intake proof....so if it will seal and FE intake and
oil pan, it will seal anything.
For gasket installation on engines that get freshened regularly, I glue the intake gaskets down in the same manner, but instead of silicone on top of the gaskets, I use a thin layer of white lithium grease.