Stretch's last comment was prophetic. I went into EPC and it turns out that the 3 piece propeller shaft is used for gasser 123s and gasser 115s. I did not check every possible iteration, but a 220 w115 (gas) has a 3 piece and a 230 w123 (gas, I picked it at random, no idea if it ever sold in the US) also has a 3 piece. The picture that Stretch included above is misleading slightly. It is in the EPC, but grayed out for all diesel model 123s. It appears that diesel 123s (240D, 300D, 300D turbo, 300CD turbo are the ones I checked) only came with a 2-piece prop shaft. If you need pictures of any of these options, let me know and I can cut and paste them from EPC.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).