My wife broke the little plastic clip that are used to hold / guide the 3rd row seat belt. I found and bought the part (part no. 16686900149051 , you can look at this picture to get a better idea which clip I'm talking about, item 4 in the pictures)

https://www.genuinemercedesparts.com.../5/5792578.gif

However it isn't trivial how to replace it. I took out the side trim at the end of the trunk (which just pop right off from pulling), poke my head inside, hoping to find a screw that fasten it to the panel. However instead found some sort of plastic peg that hold it in place, not sure how to remove it. Scared to try pry it off by force, worrying it will break that peg as well, and the peg is not listed on the part list, not sure if I can get replacement if if I break it.

Anyone tried this? Maybe I didn't describe this good enough I will try to upload some pictures when I get home tonight.