An 85TD has the newer style vacuum pump that doesn't have the hose going to the air filter, so I don't think it could be sucking oil via a broken vacuum pump diaphragm.
Checking to see if oil could be getting into the intake via another route might be useful. For instance, doesn't the oil separator return tube have a one way valve where it enters the pan? A failure in that valve may allow oil to get sucked up into the intake? I think that possibility has been discussed before on the forum.
Yes, unburned engine oil puts out big clouds of white smoke. I had the PCV system on a 67 Sprite fail, allowing engine oil to be sucked directly into the manifold. The amount of smoke it put out was a sight to see.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13