I believe I have a slight vacuum in my magnesium valve cover, I understand this to be healthy, using the intake manifold airflow to pull a small volume of air through the hoses to relieve that pressure you're experiencing.
If you still have a plastic valve cover, I think they all have an oil separator internal to it? Which may be causing problems...? If you've added a 3IM and another oil separator bolted on to it, could you possibly now have 2? RealOEM is unclear on where some hoses connect to but there are great threads on this forum.
I'll eventually be on an inner DISA repair in that area myself. Just doing a little research for now. It seems quite involved with all of the electrical / CCV hoses in the way.
Hopefully you are able to solve your issues peacefully, these cars are worth keeping alive and even better when not leaking oil all over the place.
