Carbon tracking through rotor. More HEI woes.

Need some help with a failed ignition system. I did a Forum search and found one result that might be helpful, I'll get to that in a bit.

Here's the setup:
'72 340 Mopar. Has been converted to use a GM HEI module. Blaster II coil recently replaced as part of troubleshooting. Symptoms occurred with either old or new coil.
New Taylor plug wires, 8.5mm. New spark plugs, NGK, gapped .040". (sorry can't find the part number right now, if it's important to troubleshooting I'll go out and look)

The ignition system has failed twice now. Both times a bad distributor rotor. The car runs great and after 200 miles or so, starts 'missing' and running rough. Changed the rotor and it runs great again. Decided the HEI was burning through the stock chinese rotor. Bought a tan Accel cap and rotor designed for HEI ignition systems. Again,after ~200 miles cumulative driving the engine started running rough (this weekend). Put an old, known good rotor in it (temporarily) and it runs great.

Looks like the high tension voltage is going from the rotor tab directly to distributor shaft.

Someone from a post back in 2014 here on FABO said, 'if it has resistor wires and resistor plugs, they won't do well together' or something similar. I've got both on this car.

Why would the spark go through the rotor? No moisture ever noticed in the cap. it is a vented cap.