"oil filter housing"/ block??? do you mean the one with the o-ring seal that clips in with a c clip?
If you are leaking boost from here then your PCV valve is also passing as this side of that valve should never be under positive pressure, as its the "breather" system, i.e. its technically a vented system, just re-circulated for emissions i think?
Worth replacing valve whilst you work in that area, only cheap from VW, although, saying that, I bought a brand spanker and it still passed a little, so I bought a Norgren one off ebay and piped that in, much better. (.catch can.

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