I have an 87' 240 that has excessive valve cover pressure that actually blew the head plug out.
The engine runs decent enough and has good cylinder compression on all four at around 145 psi.

Here is what I replaced with new: flame trap, small hose on trap, and breather box.

I've cleaned all of the associated hoses leading to the intake hose and did have free flow of kerosene through the hose leading to the oil pan during oil change.

I will try to clean the return hose again, but could it be worn valve guides?

The problem originated with oil blowing past valve cover oil cap.