I had a Sachs 114 with no spark and tried one of the cheap modules - for CDI ignition. It worked great and continues to this day. I think the ignition is similar to the 120.
The original igntion on the 120 was a Bosch system and was later replaced by the SEM system on the 120 Super. You can use the SEM complete system on the 120 (part number 119140210). Also as bouden says the cheap module that Rotary sells (part number 1986) will work to replace the trigger that was on the Bosch system. The trigger was 95% of the time the problem with that ignition system. Dolmar sells that module (part number 997146011).