What would make a starter motor not turn? Engine turns free by hand. Clicking sound heard when start switch pressed. Battery cable terminal on starter motor gets hot, but motor doesn't turn.

1. Battery is less than one month old; shows 12.67VDC no load.
2. All electrical connection clean and tight.
3. Starter motor removed and turns freely.
4. Starter motor opened and inspected for dirt, short or open connections.
5. Starter motor removed to bench an connected to 12VDC source, but doesn't turn.