Well, I have no experience in this but here's my thoughts.

Seems to me that the PCV system is pulling oily vapors up out from the crankcase, but the separated-out oil is not going back down.

The oil separator box is supposed to let the oil go back down. Since you replaced the box, maybe the oil is not going back down into the crankcase brecause of a clog in that pathway.

There is a test for this. Requires putting a length of garden hose, or some such tubing, onto the oil box where the flame trap attaches. Then blow through the tube while holding a hand over the oil filler hole. You should feel the air blowing through. I have seen a post covering this in more detail, but it's been a good while. Since there are two holes into the crankcase (you noticed when replacing the oil box - right?), this test may not be definitive enough. If either one is clear, you would get air through. Hmmm.

Good Luck,

Bob

:>)