Hello Drew,
there are lots of little differences with the seats indeed.
Arthur is right, the first (about) 2000 230ies had slightly different seat cushions where the left and right one are identical and not like left and right hand.
Also the backrest changed around VIN 012466 form "skinnier" (= flatter, not as thick) to later style. Also the mounting hardware between cushion and backrest changed including the chrome parts and the black backrest adjusting wheels - and many more very little details.
Rodd is right, a picture of yours would really help. From when is your car? 1965? When was it built, in 1964 or early 1965? If it has a serial no. befor 012466 (the last number before the big change in 230 production - adaptation to newer 250 S/SE sedan series), the back rests should be flatter.
And ah yes, you can find a "date" of production or something like that.
If you remove the rear panel of the seat - the one with the carpet on it (which was always the same as the rest of the carpet!!!) you can see the horse-hair upholstery (well, it's synthetic, no horsehair, rubber only) and often there you can find a little 2 x 4 inch sized paper label with the manufacturer of the padding (Emil Hauenschild, Hamburg or Fehrer (forgot what city they were)) together with the DaimlerChrysler spare part number of this cushion. The same is true for the seat cushion. But often these labels are already missing.
Please send us your picture for further details.
All the best,
Achim
(original seats, rotten leather, original two-tone carpet panels)