After a few days break to move on to other projects and think about that dying 300E, I went back 2 days ago to start/run/see if the problem would return. The owner had tried it one time and it died 3 feet out of the carport but restarted long enough to go back in.
I started the car. It ran perfectly for 5 minutes then started missing. Ran long enough for me to get the distributor cap dust cover off in time to see pretty little sparks jumping from the wire boots at various points before it died. Also a little spark
jumping from the coil wire to the aircleaner mounting. After it died, I had the owner crank the engine. Good strong spark from the coil wire but nothing from the plug wires. Yesterday, I replaced cap, rotor and wires and went on LONG test drive - car ran fine. Keeping my fingers crossed!
Happy Motoring, Mark