Give the starter housing a series of moderately-firm taps with a ballpeen hammer, where the housing steps down to a smaller diameter near the back. Then try the start pedal. If that makes it work, pull the starter and have somebody put a new set of brushes in it, or buy a rebuilt starter. It sounds like the brushes have worn too short and tapping with a hammer will re-seat them temporarily. Don't count on it working too often, though!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!