So did you identify the problem ?
Apart from the ignition coil, a usual suspect is the ignition condensator.
To help troubleshooting I would recommend:
1) an ignition dwell tester.
2) an ignition stroboscope lamp.
With (1) you can verify that the points and the condensator are working well together.
The total dwell angle should be 36 degrees at all times, all temperatures. (18 degrees for individual point unit)
With (2) you can verify that each spark lead gets the high voltage impulse towards each spark plug.
My apologies if I am writing about obvious things, but I am doing so because I know it is easy to forget about basic details when working with these fantastic cars :)
109.018.12 1968 Bronze Braun (M100 in good shape)
126.039.1A 1988 Dunkelblau (M117 so a bit slower)
+ A few other MBs used for daily transport