the car in question is a 1981 240D, I believe it is the 722.118 transmission.

Once in the past, I also had this same issue where it would not shift from 2nd, and then I found that the vacuum line going to the modulator had gotten disconnected. When I connected it again, shifting resumed as normal. This is why I am wondering if the modulator can really cause a no-shift scenario, since it seems it kinda did in the past. The modulator is for sure getting vacuum this time.

I'll look in to the B2 and K1 swaps to see if that is something I could handle on my own...

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1981 240D ... 265k
1977 240D ... 265k
1977 240D ... 250k