With the gaskets
oil soaked I would think the clamping force on the bottom of the ports has been insufficient. In that case I would look to olddog's suggestion and check the mating surface angles as well. In other words, if the manifold is tight at the top of the ports but loose on the bottom it'll seem A-OK looking from the top but will still suck
oil from the bottom. This could occur with just a few degrees variance between the head and manifold mating surfaces.
JMHO, Steve