So it's using oil only under high vacuum. Your turbo should have a restrictor already built into the CHRA.
Have you thought about checking the breather system one way valves. You could be sucking straight from the crankcase into the inlet.
i have been having a trial fit/test of the new breather system
i blanked the T piece off that comes from the crank breather to inlet manifold and fitted the breather system/tank as everyone else has
the smoke with that little bit extra vacuum thru to the turbo was unreal and i had to stop driving it
i then refitted the T piece back into breather system and into inlet and had no smoke for quite a while although i did notice a some after about 300 miles
deffo think turbo is kapput now
i have also had a comp/leak test done thru a vag tech mate (on dealer equipment) and all was fine