Maybe this would be a good time to buy a CD Factory Service Manual.
Mercedes does not list a CD-ROM shop manual for the 300SD but the 300D version will at least have the same engine (617.952 in the 300D, 617.951 in the 300SD). The 300D manual is QL-6516-5610-02 for $19.99. Shipping was $6 to my address.
http://www.classictechlit.mbusa.com/MB/default.asp?catalog_name=Retail&cookie%5Ftest=1