Gleitpaste
A "Tub" will do about 150 cars,and is horrendously expensive.
(Made for use in dealerships)
Almost all vendors will sell you a small amount needed for personal use.
(Our sponsor, P.P. , will set you up with enough for a couple of "Roofs" for
a reasonable price.)
[Thanks to GSXR for the Photo]
http://www.w124performance.com/images/W124_sunroof/special_lube.jpg
Sadly the contact info in the picture for the source is now un-obtainium.
Link to the pictures of sunroof "Sliders" that go on your Neked metal tabs:
http://www.w124performance.com/images/W124_sunroof/sunroof_sliders.jpg