MB designed a backup system in case the electrical power sunroof fails. There is a nut accessible in the trunk, same size as the lug nuts. You can use the lug wrench to turn the nut and close the sunroof. However, you may want to leave it not fully closed until after you close the deal. If you show the owner how to close it, he may not be inclined to cut the price.
If you are new to Mercedes, and new to diesels, you might want to make this your homepage. There are some true experts here.
What has impressed me--I've owned a lot of different cars-- and I have always done all my own work---is the obvious thought that went into most operations by M-B. As you DIY on various projects you will see what I mean. The engineers have thought through almost everything.
Use the search function to find old threads before starting a new question--do not ask ANY oil-related questions. They have ALL been asked before--with more heat than light being the result.
Anyway, welcome to the group. since the Off Topic Thread has been closed, no one here will bite.