[Charlie Stylianos]

Does tapping on the solenoid (the small lump attached to the starter) help the situation? Grease, dirt, and heat over the years can make them act intermittent/ineffective. Usually a sharp wrap will free the mechanism until it fails again.

Also, faulty connections can cause this. Check the ground strap from chassis to tranny, and all the electrical connections on the starter for corrosion on the terminals (disconnect battery first). I remember RL's starter had the exact same symptoms, could not find the problem, so when we were replacing the starter we found the little yellow wire to the solenoid had a good inch of corrosion within the insulation. A splice and solder fixed the issue.