If you are referring to the seal that fits into the chassis and is situated along the top edge of each front side window and rear side window...

...for my two 300 CDs ('83 - no longer have it and '85 - still have it), the seal is one piece for each side of the vehicle. This is based upon the two seals (left and right) that I acquired directly from M-B (re: "Also I've seen pictures of these seals that appear to be one long piece instead of two pieces per side.").