Intermittent No start.

Hey All. I've had this issue for a few years now. Every once in a while I get these no start situations on my 72 Plymouth with factory electronic ignition. I'm talking once every 3 months or longer. Sometimes when the car is hot and sometimes cold. In the past I have had luck changing out the ballast resistor but did not test them afterwards (away from home deal). I made sure I have bare metal mounting and added additional grounding to the Ign module and the voltage regulator and use dielectric grease on the connectors. I had the issue this weekend and found no spark out of the coil. Swapped the ballast. NFG. Put the old back in. Swapped the VReg (wanted to replace anyway with adjustable) NFG. Left it in. Had a helper crank so I could test and went from no spark to nice hot spark. Car started and ran great ever since. Now I really doubt it was my ballast resistor all along and just luck. I'm also 90% sure I have replaced the Ignition Module since this started as well. The one thing that I do know is that during almost every no start is that after cranking and stop, then releasing the key 1 position, the engine turns over maybe half a turn (not sure forward or back) and I get a slight pop of gas through the carb. I'm kind of thinking I have an ignition switch going on me. I'd like to get nailed down before it leaves me stranded but I guess at least I could diagnose. Anyone ever experience this?
Thanks.