It should not be too hard to see if it is the Turbo ornot.
Some thoughts:
First remove the Air Inlet from the Turbo.
Observe what it looks like inside, do you see any broken Fins on the Wheel; is the Shaft Nut still there and tight.

Reach in and spin the Turbo Compressor Wheel and see if you can feel it bind.

Next push the Wheel towards the rear of the Car and rotate it with a slight pressure and see if you feel any binding or dragging.

Move the shaft back and forth side ways. When you do that it shold not make contact with any of the Housings.

Do the same but pull it forward as you slowly spin it.

Push it in and out and see if there is a lot of end Play. When you do this it should not "thunk" when you pull it in and out.

Finally you know that Oil was coming out of the Exhaust Pipe so you know there is going to be Oil in the Turbine Housing of the Turbocharger. But, what will tell you where the Oil came from is if you remove the Turbocharger.
If the Exhaust manifold is dry you know the Oil did not come from the Engine and it has to be a problem with the Turbo.

If the Exhaust Manifold is wet I would suspect something like the Member who had a Valve Guide break. I guess it would have to be an Exhaust Valve Guide.

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84 300D, 82 Volvo 244Gl Diesel