You can get the MB anti-squeal grease from this site. See here:

http://catalog.peachparts.com/ShopByVehicle.epc?q=1998-Mercedes--Benz-S3--0--Lwb-Brake&yearid=1998%40%401998&makeid=63%40%40MERCEDES+BENZ&modelid=6432%3AMBC|1587%3AED|214%3ASM|672%40%40S320+LWB&catid=241658%40%40Brake&subcatid=241665@@Brake+Anti+Squeal+Paste&mode=PA

If your working with larger pads/calipers I'd get 2 per wheel instead of one. It's pretty cheap. (~$1.50)