You are absolutely correct in your statement that the FI Pump is lubricated by engine oul.....in the lower half....the part containing bearings and camshaft, and engine oil also lubes the governor.....

BUT

The upper half...the pump plungers and barrels and delivery valves...are ONLY lubed by the fuel being pumped...whatever that fuel may be....those parts are all metal to metal, machined to fit, precision, ultra close tolerance parts.....thus the threads around here relating to concern over lack of lubricity in ULSD....

Photo below is a cutaway of a Bosch Fuel Injection Pump of similar type to those used in your Benz....



Photo Courtesy: Diesel Engineering Handbook 12th Edition; Stinson (page 86)

Another cutaway of a Bosch Fuel Injection Pump of similar type to those used on your Benz....



Photo Courtesy: Diesel Engine Reference Book, Lilly
SB

FYI....ALL Fuel Injection Pumps, no matter what the brand or design are lubed in this manner....as well as the metal to metal parts within the Fuel Injection Nozzels (Fuel Injectors).....those parts are called needles and guides.....

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG