that have not had sunroof maintenance that is common this time of year.

Since it is closed, leave it alone until the weather warms. You will find it will then open enough for you to perform the needed maintenance. The jam is probably caused by old, stiffened grease or no grease at all.

You will have to pull the sunroof headliner (not difficult) and remove the cable. Then you can clean the old grease out/off of the cable, guide tubes and slides and relubricate.

Instructions, tools and the proper greases can be obtained from Mercedes source dot com as a kit. This is a needed maintenance job but not very often. Maybe every 5 or 10 years.