There are plastic pegs and the matching plastic collars break over time. They are inexpensive dealer items. Open the sunroof about 1/3 and use a butter knife to pry the cover loose--pull forward and down. Check the condition of other plastics parts while the cover is off. There are several good SEC sunroof repair articles recently posted in the mbcoupes.com archives. Cheers, Andrew Seidel.
85 500SEC Lorinser
83 300D Turbo