I'd check at the coil wire. So far as a coil "is either good or bad" Coils are FAMOUS for running when cold, failing when hot, so the comment the "coil is on it's way out" DOES HAVE some merit.
Condensers (the one in the distributor, remember?) can do the same thing.
Condensers can develop all kinds of irritating problems, cheapest thing to do is just replace them.
