[classical glass]

While taking apart a 65 427 Side Oiler I pulled off the MSD distributor cap and noticed it was loaded with some sort of a carbon dust.I took it off and cleaned it out the best I could, replaced the rotor and cap. I put on a GM cap with brass contacts thinking this might help. My question where did all this carbon come from? Its a fair weather car driven only in the summer on sunny days. It's a MSD # 8594 with a 6al box. The car runs strong with no issues but something isn't right here. any input would help.
Thanks