Starter stuck!

[65sbss]

I have a 350 with Hei ignition. Recently I went to start it and I got the "click" like it was bad solenoid. I took out old starter, installed new one and it started fine for a couple of weeks. Then it did the same thing, click and no start.
I took it to shop and they put in new starter. and he said gear is not disengaging flywheel (burning up Starter in process.) He is very experienced. They shimed the starter. Still will not disengage. Flywheel looks good. Teeth ok and about 14.1 dia. I noticed the thin yellow wire to starter had burned slightly. Could bad ignition cause this? I appreciate your help!