stalling 1998 88 no/sc

My daughters 88 has stalled on her three times in the last three months. The first time it happened I diagnosed missing spark from the bottom coil on both plugs. No problem I have a 1998 LSS so I swap the coil but no go, then I swap the ignition module and vala, car starts. The strange thing is I throw the bad ignition module from the 88 back in my car for yuks and it runs. I am scratching my head, maybe there was some moisture on it, I don't know. Well it has done it two more times and all I do is pull the three coils, rub a rag on the ignition module put everything back together and it will start right up. Kinda at a loss, any ideas appreciated.