Could be anything from knackered turbo to worn piston rings really. It is normal to have oil in the boost pipes especially as your breather is connected to the inlet. Cossies are also prone to that. My first Cossie had a standard air box with the breather attached and there was oil inside all the breather pipes. On my current cossie I have a seperate breather that does not go back into the inlet and now I have no oil in the boost pipes. If your engine is breathing badly then that oil will go back through the inlet and burn with the fuel/air causing your engine to smoke a bit.