I've found the most common places are near the connectors where there's no wire sheathing. The insulation on the wires gets old and brittle. So I'd start with a visual inspection of the wires around your distributor, coil, and power transistor connectors. Repair and insulate and bare wires.
At that point I'd break out a multimeter and check for continuity between the various ignition components and also with the ecu. Best method would be test it right after it starts acting up again. While you're poking around I'd also test the resistance on the coil and power transistor to make sure the components are within spec.
That's where I'd start. Hopefully this gives you a direction to go in. Worst thing is having an issue and not knowing where to start!
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