Intake Manifold Installation

I would guess that the oil is escaping from the front and back block and intake seams as you stated. If you read the installation procedures that came with the manifold they tell you to throw away the cork gaskets and just use a bead of rtv.I'm not sure why they say to not use the gaskets but, I'm sure there is a good reason.
I did the same thing on a performer intake a few years back. I installed the intake and had oil coming out of the seams. I didn't use enough rtv to seal it. I think the only way to fix it right is "remove and repeat". At least that's what "cured" mine.I used a pretty good sized bead of rtv. Actually I think I laid one bead on top of the first bead. My thinking is that too much is better than not enough. I don't think there is any issue with having too much rtv along the seam as it will just flatten out as it's compressed.
I'm no expert on the subject and If I'm wrong on this I hope some of the others here will chime in and help you out too.