1974 Mercedes Benz 450sl Car turns over but will not start

I have been chasing a starting problem for several months. The car would turn over but would not start, as though there was no spark. My local Mercedes Club technician finally traced the problem to the transistorized ignition control module (the car would start and run fine when a condenser was used in place of the module). The module was replaced, along with replacing the new Bosch coil with an older available coil (the new Bosch was returned to the auto parts store because it was said to be bad). The car ran fine for a week, starting every day with no problem. After sitting without starting it for a couple of days, it would not start. It would act like it had spark, but not sufficiently to catch and run.

Eventually I replaced the coil with an available coil I had run the car with for four years. The car started immediately, ran for that day and the next day with several starts and stops. After sitting for two days, the car would not start - acting like there was no spark at all going to the cylinders. Last resort was to replace my old four-year running coil with another new Bosch coil, with no apparent success in spark to the cylinders.

I am wondering if I should go back to a points-and-condenser setup on this car and avoid the transistor setup, resistors, etc, or is there some kind of intermittent circuit problem that is causing this? I don't have enough money to continually chase a ghost of a problem, and AAA is getting tired of my free towing calls.