One word. Plenum. The magnum engines are known for blown Plenum gaskets. There's a kit you can get to fix it. I did it and its actually pretty easy to do as long as you have some mechanics know how. The Plenum sits between the engine and intake manifold. Dodge made the manifold aluminum and Plenum plate steel. The temps between those two metals is way different and eventually causes the gasket to blow. That more then likely the problem imo. Way you can check is to take the intake off the throttle body, open up the blades and look down the throat of the throttle body with a flashlight. If there's oil of any amount in there, you got a blown Plenum.
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