not sure on what setup.. etc etc. mine the turbo was getting a tad to much oil pressure, not large enough restrictor, and the BOV was developing an oily film on it from some coming throught the compressor seals into the charge tube. if you can actually see it.. probably worth checking into it. pull of a charge tube, bet it has a LOT of oily residue in things.
for a diagnosis of where its coming from, whos kit, milage.. etc etc.
Does your blowoff valve have a brass plunger? If so then it's probably brass dust. If its gold then you should save it...its worth like $1100 an ounce.