I had a B20 installed from a 1973. The old B18 only had a dump tube on the flame guard and that is how the B20 was set up also.
I read in a SWEM article with PCV diagrams that when the extraction path is blocked, it leads to crankcase pressurization and oil leakage around the filler cap. This statement is what caught my attention because that is exactly what I have.

When I look at the B20 diagram, my dump tube is sucking air, just like the diagram. The only difference is that the air is not going through the air filter first.

The difference is, my oil filler cap is solid si it seems to me, there is no extraction path at all causing the leaky filler cap.

If this makes any sense then I think I need to put on a oil filler cap with a tube to the intake manifold and the problem is solved?

Could it be this easy or am I missing something along the way?

DC