Along with all the other helpful hints, here's what I had to do just this week on my D-14.
After installing new battery, cables,starter solenoid,new wire to starter switch,wire brushed starter housing real good,new bolt...once very 4 or 5 times all I got was a 'click', starter wouldn't go round. "Magically' removing the starter and puting it back made it work again,that time.
Finally got fed up with that routine, so I took the starter off and popped of the rear housing.ONE on the brushes was TOTALLY worn out ! It was probably damaged 20+ years ago( it sat for 'awhile'), maybe that's why I got a good deal on it.
Anyway, I took the end cap with the brushes to a local auto electrical repair shop. For 6 bucks they installed a new brush,screw and resoldered a bad wire.
Now Alice starts EVERY time with much more zing than before.
hope this helps
Jay in Greensville,Ont.