120k miles is nothing for the DW12, it's capable of well over twice that distance with regular servicing. Oil in the intake is normal for these. If there's a problem with crankcase pressure, then release the oil filler cap and let it sit on the filler loose while the engine is running. If it stays put, the engine is fine, if it blows off there's an issue.
Have you checked to see if the air intake pipe is leaking where it joins the turbo down pipe? Normally the factory hose clip stops sealing, allowing oil to drip down into the turbo making an oil burning smell inside the cabin. Replace the factory clip with a proper worm drive clip, and ensure the seal isn't flipped before tightening the hose clip and the oil smell should go away in time.