weird oil leaking rear main seal or oil pan arch - maybe PCV valve

Crank case pressure, overfilled, not very tight pan seal could all add up to a leak at the rear of the pan.

It could very well could be something else, but it also could be exactly what you think it is.
Try tightening up on the rear most pan bolts just a little if it feels doable, then try to get some block venting even if a temporary test.