Had a similar problem with my '65 Mustang. I had degreased and washed down the engine. When I drove home it was fine. Went to start it the next morning, and you guessed it, moisture in the distributer cap. Spayed in some WD40 and was on my way. Everything was fine until I was on my way home that evening. It stated misfiring badly when I got into the gas. I had filled up that morning at a different station. So I got some Sea Foam on the way home, but it made no difference. Pulled the top off of the carb, both float bowls were full and clean. I pulled the plugs and they were a mess. So I replaced them. A friend has suggested that the rotor may have arc traced to the distributer shaft. So I replaced it too. Took it out on the road, kicked in the secondaries, problem solved. Well Driving to work the next morning (35 miles), I got within 2 miles of work and it all started up again. Tried nursing it home that evening and got about 1/3 of the way home and it was really getting bad. Stopped and swapped out the distributer cap (just happened to have a new one with me). No joy. I got within 6 miles of home and it died at a traffic light and wouldn't fire. Had to be towed home. The only time it had let me sit in the 13 years I've owned it, driving nearly every day. Well, since I was running an Ignitor and the wires were fairly new, the only thing left was the coil. Bingo. Been running like a top since. Looking at the old coil, I believe it was the original.