Starters are pretty stolid machines. Likely that some other component has gotten tired.

The starter drive gear mechanism, sometimes call the Bendix, is supposed to retract the drive gear when the engine speed is high enough. If it cannot retract, then power to the starter motor is not disconnected, and the result is what you experienced.

When the Bendix drive is old enough (like an 81) the grease may be just too stiff for proper operation. It will engage - powerfull magnet pulling the gear into the flywheel ring gear. But when it is supposed to retract, only a spring is pulling the gear back, and maybe it cannot overcome the stiff old grease.

Have handy a long iron rod or a series of 1/2 inch socket set extensions. Long enough so that you can place one end on the starter solenoid housing and whack the other end with a hammer. The idea is that if the starter won't release, a whack or two may jar the thing loose.

Repair will likely require removing the starter - check the FAQs for tips.

The other possibility is the ignition switch. But you already tried that, right?

Good Luck,

Bob

:>)