[iceminion]

I also have this problem, I am quite perplexed.

I have also replaced the o-ring.

my best guess is there is excess pressure from boost/valve train/blowby and for whatever reason it is not getting vented out the breather on the side of the valve cover.

my plans are to re-connect my breather to the intake side of the intake pipe, one so the metered air is accounted for, thus resulting in running smoother and second so that there will always be vacuum in the valve cover.

Just because something leaks doesnt mean that it directly is the problem.