check all to the plugs on the head. I think there are 2 on each head, maybe 3. Check the lines from the HPOP to the head and check the
IPR on the side of the HPOP. The
IPR is a typical part that needs new O rings once in a while. Also check how tight the turbo pedestal bolt are. If the turbo works loose, there are two O rings in there that can leak. If those parts are all good then it could be the rear main seal.
Let us know what you find.