Keith;
I assume your starter has the solenoid on top of the starter.
If so, when triggered by the signal wire from the Ign. switch, it pulls the gear into the flywheel. and makes the starter spin. This is done by a copper disc on the end of the piston inside of the solenoid.
This disc gets pulled against the contacts at the end of the solenoid and bridges the Positive Battery cable attached to the solenoid to the motor itself. The cable attaches on the outside to a stud which becomes a contact inside. Inside, below this contact is a similar one and the copper disc bridges the two.. This provides the motor with the current to run on.
The repair is as simple as taking apart the solenoid, removing the copper disc and rotating it 90 degrees, thus providing 2 new un-pitted surfaces, as new.
After many years of service, this can be done again by reversing (flipping) the disc, to start over. Thus giving you 3 times you can repair it this way.
Lube the Bendix while you have it out, being sure the gear not only spins out OK, but will return on its own to the un-engaged position.
Hope I haven't bored y'all with this, but some have no idea of how solenoids work.
Ray