OK . . . I had the same exact problem on the same exact engine . . . before you look at lift pumps, IP rebuilds, etc.:

1. start with fixing the obvious, and usually the cheapeast!!! Before you go past "GO," replace all of your return lines and bleed the system. You would be amazed at how much is actually leaking and may be the entire cause of the problem. The old return lines get eaten up by the newer diesel fuel, and have to eventually be replaced by the new stuff that is reformulated. This is where my problems stopped on my 190D.

2. However, on my 240D, it was less of a problem, but not the entire fix, and I had to go to step 2. If you still have a leak, look to see if there is pooling under the injectors . . . if so, time to remove your injectors, put on a table-mounted vice grip and snug them up, replacing any o-rings or snap rings that may also be required. If there is no pooling from the injectors, then go on to step 3, which should also be looked at immediately.

3. Check every clamp, hose, and tubing go make sure there isn't any leaking from connections to and from aux fuel pump/primer pump, pre-filter, clear in-line filter, etc. Trace the entire fuel path under the hood of the car. Make sure the tubing isn't leaking where it's connected to the IP or Injectors, and anywhere else they connect. After you have eliminated all that, and only after all of the has been replaced and eliminated as a source, should you start looking at pump, or IP, and if it is either, make sure it's not simple mounting gasket, first. Never mess with the IP adjustments unless it is last resort!!! and then only, if you have a backup plan!!!

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1983 300D, the "Avocado"
1976 240D, 4-spd the "Pumpkin", SOLD to Pierre
1984 190D, 2.2L, 5-spd, my intro to MBZ diesels, crashed into in 2002