B and RB Chryslers are very fussy here.
Reusing the valley cover is not really a good idea.
There are sealing ribs stamped into the valley cover to aid in sealing>>>>>
These are a one time use cover.
Also----the sealing surfaces of the head and intake need to be true---and absolutely clean before install------I always used a bit of coppercoat on the both sides of the cover to help seal.
Your oil could very well be coming thru the intake ports.
Might also check the valve cover gaskets---maybe a leak in the top middle of the valve cover.