SOLVED!....sort of. Where's there's spark.. there's no fire!

Have you checked the inside of the distributor cap for wear and electrical tracking?
Is this a coil mounted on the distributor cap? If so the contact between coil and cap could be worn out. Distributor cap if like this you need to check the center point.
Remote coil? check for a crack tracking on high voltage lead along backlight. This is on some later models.