The rocker cover design inside is designed to separate mist from the crankcase 'blowby', there will always be a slight positive there and it brings the oil mist with it. It's designed to re-burn that oil mist and can often be seen in the exhaust smoke if the engine has been idling for while. Valve stem seals can show the same symptoms but this is more prevalent in petrol engines that have a strong vacuum caused by the throttle butterfly, something the 80 diesel does not have. With such a low mileage it would be unusual that either the turbo seals or the valve guides are worn, unless it has been severely mistreated.
I agree with Shane that the engine should only be burning air and fuel. if it is to be efficient, I would do as others have said and remove/seal up the pipes and consider the 'catch can' which TBH, should not be needed again with such a low indicated mileage. Something that I did not see mentioned (just flicked through) is dirty injectors, or injector timing, this too can cause the grey/blue smoke in fact, if the injectors are dirty/faulty or timing is wrong, then this can lead to excess fuel being left on the bore walls or, when the engine is off an injector could continue to drip diesel into the bore. The result is the diesel finds it's way into the sump and the oil becomes slowly diluted. When the engine gets hot, the now lighter oil mist particles find it easier to transit through to the air intake, this thin oil can find it's way past pipe connections where the clips have lost their tension, in the worse case scenario I have seen on an 80, is the main intake pipe has actually become porous.
I have found that engines (even in excellent condition) that get pootled around town for a few days a week tend to build some oil residue in the air intake or lying in the lowest area of the intercooler (not on your 80), a quick blast down the motorway clears this out. Remove the pipe from the rocker cover and place a cloth in front of it and rev the engine a few times, a
gentle if any pressure will be felt, any more than that there you have an internal engine problem. The cloth should pick up just the minimum in oil 'specks'.
The turbo oil pressure feed to the turbo bearings is also kept sealed away from the intake/exhaust, thin oil can also pass into the hot exhaust passage and this too can cause smoke.
Just throwing this out there in one go so you have something to do over the weekend, can't have an 80 parked up with no one working on it.
regards
Dave