I also believe that a knowledge of the German language would be an asset here. Someday I should learn it.
"W" always seems to be a reference to a sedan body style. One thing I do know is that the V is for Vito, which is used in reference to the longer S-class chassis as opposed to the short wheelbase S-class. An A I believe is a convertible, or possibly a coupe. At any rate, the letter is a designation for the body type. In some literature, the old SLC's were referred to as a C107 instead of an R107, same with the SEC's being called a C126 instead of a W126.
Gilly