Young1 There might be a problem with the surface on the manifold where the distributor goes through it.
Quick questions, Can you turn the distributor my hand with it bolted on the manifold? If yes may need to get a stronger retaining plate or new one. If no lets look at the bolt that retains the fork on the housing and add sealer to the threads and retork to spec. If this doesn't change anything and it still leaks lets start the motor and to a couple of revs to 2,500 rpms and see if blue smoke or any smoke comes from the valve covers Make sure the PVC is also sucking. If all this checks out,
Iwas going to add dye and find where the leak is coming from. We have had guys think there rear main seal is leaking and it turns out to be the
oil pan from the front of the motor.
The last thing is how much machine work was done to the block, heads, and manifold. Where the gaps the same on both sides front and back of the motor. I am thinking the intake manifold may have shifted and added stress the the distributor and causing the leak. With distributor out, pull the
oil pump drive and check it for wear. Sam with the gear on the bottom of the distributor. May be worn out and causing same problem. Might want to replace the gear even if it looks OK. PS I had nothing but problems with Mallory and went to Accel and then MSD. Good luck Rick L.