You can replace the brushes if you are mechanically inclined and have some soldering skills. Though, with a 70$ core I'd just replace the starter. An old timers trick is to whack the starter while someone holds the key in the start position. If the starter begins to work, blamo, need a starter. However, this wont diagnose all starter related problems so you may still need a new starter if the whack trick doesnt make the car start.