(DISCLAIMER: I know [And want to know even less] NOTHING about Gasoline/Petrol/Benzine Mercedes.)

The Engine Oil (Sump) Dipstick has a nice little rubber "O" ring to seal the Tube
AGAINST acquiring and Dust, DIRT, or other Contamination.
If the "O" ring is Old,Dry and Brittle and has Shrunk from it's original Thickness;
it MAY allow SOME Crankcase Gasses and Pressure to vent through the no longer sealed "DipStick" tube.

[REMEMBER the DISCLAIMER ? Mercedes COULD have some Extreme Walter Mitty
device that senses loss of "Blowby" and corrects for it through Electronic Wizardry (?)]
[Although, WHY they would do such a thing would not be able to be explainable in the Physical Universe we inhabit!]

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'84 300SD sold
124.128