Yes, they are difficult to remove. I gave them a shot of PB Blaster then pulled the clip with pliers. A flat blade screwdriver placed carefully under the head of the pin and tapped upward carefully got them moving until the pin could be grasped by pliers and worked out.

IRT part availability; I found the rear door check also very hard to find. No surprise since it is the same part number. I did find Meyle aftermarket items on mercedes source dot com and ordered two.

Note: name of source modified to allow identification.