I had the same problem... tightened up the injector lines (could see a slight fuel leak => air leak as well) and also replaced the primer pump (was also leaking air/fuel). I'm not sure which of these fixed the problem... just go ahead and replace the primer pump... it is cheap and easy to do.

If you can see fuel leaking then air is also likely coming in... you can clean off the fuel system and look for what looks like oil (i.e., diesel) and fix the problem from there.

As a side note my fuel mileage improved noticable (by 1 or 2 mpg) after the above were done

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1985 MBZ 300DT
1969 MBZ 220d
1984 MBZ 300TDT
1981 VW Vanagon