it could be the turbo, what i'd do is find a friend and pull the turbo off, then get your friend to hold the oil feed pipe in the oil return pipe in the block.
then run the engine without the turbo/manifold.
if it smokes it is an engine prob, if not then the turbo is to blame(ish)
check the exhaust elbow off the turbo for oil and the manifold where it bolts to head for oil also.
check the exhaust ports too for oil, you will have soot, but if you wipe your finger over it, if it's oil it'll stay wet, if condensation/overfuelling then it'll evapourate and leave a dry soot.

it could be the rings in an oval bore sadly, but you won't know till you've satisfied yourself with the turbo.

hope that help.