You've got worn-out brushes in the starter motor. Try this- - - -have someone hold the ignition switch in the "start" position, and reach underneath and give the starter a good whack with a hammer. I'll bet it starts, at least a few times, before the problem comes back. The "pull-in" winding on the starter solenoid grounds itself through the main starter motor. If the brushes don't get a good contact on the commutator, the "hold-in" winding that goes directly to ground doesn't have enough power to pull the drive gear into mesh and engage the contact on the back of the solenoid. I've seen numerous solenoids changed fopr this problem, whe the real problem is actually in the starter. The "dead winding" problem results in a much harder click, because the solenoid actually engages, but the starter motor doesn't turn.
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!