Hi -- you have posted in a forum that comprises people that have cars
without rear doors. You might want to post in the "Tech" forum where you will probably get learned replies for your type of MB from others with the same or similar vehicles. While I am sure that there are members here that can help you, you'll find a lot of information at the following link:
http://www.peachparts.com/shopforum/forumdisplay.php?forumid=1
also, try this (found in a search of the above forum and suggested as being similar to rear door panel removal):
http://www.peachparts.com/shopforum/showthread.php?threadid=67259&highlight=door+panel
Best of luck!!