I have noticed a few things on my 500SEL (i know, not a diesel). If I check the oil cold I get one reading. If I check at a fuel stop after running hard for a few hours, I get a higher reading. I assume it is because of the 8.5 quarts of oil expanding like the transmission oil does. So, any time I check the oil, if it is between the lower mark and the higher mark it is fine.
The other thing I have found is if you wipe off the stick and reinsert it and pull it back out quickly the reading is lower than if you reinsert, wait 10 seconds and pull and check again. Since the tube goes all the way down to the bottom of the pan, the o-ring at the top of the stick acts like a plunger, pushing the oil down in the tube and making the level lower in the tube.
I have never noticed this on my 300D mainly because I seldom run it long distances and also have the habit of waiting 10 seconds like on the other car.
So, just check it and think about the conditions at the time and every thing will be fine.

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84 500 SEL (307,xxx miles)