No one agrees with me but you can coat them with Super Corona Dope, a very high voltage insulation that looks like clear finger nail polish from MG chemicals. Once the cracks are filled wrap with radio controlled airplane very thin fiberglass cloth & recoat. What is the resistance from plug wire to ground? Once the coil is clean look for pits where the coil may have arced to ground. There is two coil windings, primary &; the secondary winding, the wire used is finer than a humane hair & damaged easy. Running without having the plug wire off the spark plug has produced energy & will arc to the magneto plate.
Also don’t forget the capacitors, they fail too & will not give a good spark. They are 2 pieces of foil separated by wax as an insulator. The wax shrinks with time & shorts out the foils.
Top seal may be bad blowing fuel on the magneto causing no spark too, was it wet?
