I had success to solve this problem by replacing the two rubber elbows on the vacuum line that runs from the left hand side of the intake manifold to the recirculation valve located deep down on the air inlet duct at the turbo intake. You must ensure that the vacuum tube is not clogged also. Theses tubes are brittle (plastic), hence handle with care. The valve must be cleaned and especially the hole on the side where the rubber elbow connect (smaller one). To work on the valve and clean it, it is easier to remove the duct assembly. I found that the rubber elbows become contaminated by oil and soften. Their walls collapses and stick on each others which block vacumm air circulation which in turn augment positive crankcase pressure. Changing the oil separator (located under the intake) seems to me unecessary. I hacksaw mine to find no blockage. The trick is to have integrity with your tubes and vacuum down to the valve. This will ensure positve draw of fumes to turbo intake. This is good preventive maintenance that cost a few $ but save hundred. Good luck! My car is a S70 T5 1998. NA can be different.