I put several thumbtacks on this one a few months ago. From the front seat it looks ok; from the back it looks awful. If I continue with this temporary measure I may paint the thumbtacks to match the headliner.
My headliner is mostly vinyl (same as on the sunroof sunshade and the visors), with cloth on the edges that matches the pillars.
A couple of years ago I redid the sunshade, which had failed first. It wasn't that tough to do (though I can't say it looks as smooth as it should), as the panel can be removed from outside the car. I just put the beige headliner fabric from JoAnn fabric on it, after cleaning up the board. When I reinstalled it I realized that it was thicker than what was originally on there, but I felt it was tolerable.
In researching this recently, I have come to learn that MB headlining material is 1/8 inch thick, and American headliners are typically 1/4 inch. This can cause problems if you redo cars with sunroofs in the thicker material.
BTW, some online sources and resources include:
Headliner Express Home Page
World Upholstery & Trim: USA Manufacturer and Distributor of European Auto / Car Upholstery (Apparently the most current url for World Upholstery)
GAHH: Convertible Tops, Auto Interiors, Quality Convertible Tops
From the headlinerexpress site, I gather that German vinyl is available, which in conjunction with 1/8 in. foam is the way to get the original look and fit. I still don't know if it is possible to clean the crumbling foam off of the original headliner, and reinstall it over new foam. I would doubt that it's possible. I must have thrown the material from the sunshade away, otherwise I could figure it out.
If I pull the headliner out, I can either recover it myself, or take it to a professional. Putting 1/4 inch material on it shouldn't matter, but I am concerned about the sunroof, so I would like to take the thick material off of the sunshade while I'm at it.