Originally Posted by DCF

Maybe my 99 ml 430 is different, but mine are held on with one piece clips that are slightly greenish, but still basically white plastic. You pop the door panel off, slide new clips into the panel, and then you line up the points on the clips with the holes in the steel door frame, and give the panel a good firm smack over each clip. That sets them in. To replace the clips you really need to totally remove the panel. Oh, and when you do that, you may break off a few more clips, so if you go to the parts store first, buy a few more than you need.

There are instructions on the site on getting the panel off, it takes all of about 2 minutes, tops.