On my '95 E320 wagon there is a black plastic retainer holding the headlight assembly to the body. "Holding" is the wrong word: The headlight assembly is held by three screws, the plastic part is just inserted at the top. MB part number is 124-821-05-20, description is "Insertion, Li". It is removed using a 1/4 ccw turn and installed using a 1/4 cw turn. It's so fragile, it usually breaks. It's cheap: $4.18 ea list. On my car, it was marked by a red dot made using paint, with a corresponding dot on the sheet metal adjacent. The book, oops, the CD, doesn't explain the function, just how to remove & install.
Enlighten me, please!