If you suspect the intake/pan gasket leaking, try this test.
with the engine running, remove the oil fill cap and lay a thin piece of paper-like a napkin-- over the hole. It should pus out, NEVER draw in. If it draws in the gasket most likely is the problem.

BTW, I owned two different magnum engines that had the gasket changed under warrantee.
both still leaked and I got a good deal on those trucks.

Pulled the intake and found the 'mechanic', 'trouble shooter', 'parts changer, didn't pay attention to his own work.
On both, the bolts bottomed out before the washer contacted the pan on MOST bolts.
Apparently the holes were not drilled deep enough!!!
I simply added two washers to each and checked each before final torque.