Toasty, use the fsm starter test procedures to test the windings. Bet it's just brushes, but starter rebuilds, even having the thing rewound, are not very expensive at a good shop. Try elec motor rebuilding shops. Brushes are cheap. The most likely failure point is the solenoid internal contacts that carry the heavy juice, and sometimes the solenoid windings themselves. How is the starter gear?

You can test the starter motor easily with jumper cables. Ground the motor frame to a car battery with the black cable to batt-. hook the red to battery +. Touch the red to the lower solenoid big bolt connector, the one that's hooked to the motor windings. motor should spin, but solenoid will not extend the gear. Now test the solenoid. Same black hookup, but hook the red to the upper solenoid fat terminal. Use a jumper wire from the red to the solenoid terminal (usually the spade connector or the smallest connector). Solenoid should extend the gear, then the motor will spin the gear. If not, remove the two jumper cables, and ohm the spade connector to frame or solenoid case. Should be an open circuit - if not, solenoid windings are bad. If test two does not extend the gear and spin the motor, the problem is that the solenoid core is not completing the circuit between the two fat terminals on the end of the solenoid. This is usually due to arc scarring of the copper disk or fat terminal ends, and if you can take the solenoid apart, you can clean these up with emery paper or a file. In any case, a solenoid is a lot cheaper than a starter.