I just discovered something.
My readings with engine off:
Pin 1 & 2 AFM untouched: 4,7kOhm
Pin 1 & 2 max resistance: 16kOhm
Pin 1 & 2 in between: except idle deflection continuously rising resistance with rising deflection until max then falling - at the upper measure points the resistance falls off 1-4k after a second (digital multimeter)
Pin 1 & 3: always 4,13 kOhm
Now, how can be 1&2 > 1&3? Since the trim pot is serial to 1&3, 1&2 must be smaller 1&3 unless there is a further resistance at 2. So maybe the contact of 2 has a serious problem itself (dirt) and not only the layer on the pot?!
How did you notice that your new pot didn't fit. "Just" because the engine didn't run as well anymore or did you measure different resistances or anything else?
By the way, its a 300SL from 86