From what I read in a German forum, the trunk lid of our cars was originally equipped with two stick on pieces of plastic. Right a the two front edges, these were supposed to slide across the plastic knuckles on the car’s body.
The stickers are rubbish, so in daily practice it’s your trunk lid against the knuckles, resulting in paint damage and wear out of the knuckles (eventually to an extent where the bolt takes over).

One day, MB came up with a less flimsy solution: part number A2309870120 (L) and 0220 (R), a more solid plastic slider with hopefully more ruggedness. Part number 100 in the drawing.