Originally Posted by Capt J
I am not familiar with your windlass, but it sounds like the motor is the culprit if it has no issues going up.
considering that it's a DC motor with one set of brushes, one commutator, and one armature, and one field, and works properly in one direction, and knowing that the only thing that changes when reversing direction int htat type of motor is polarity, a reasonable troubleshooter would have a look at the device that changes the polarity.
That device is called a solenoid, it mechanically moves a set of contacts that change the polarity of electricity delivered to the brushes. If the poster hears the solenoid click then a reasonable troubleshooter would examine the condition of the contacts associated with that solenoid. This can easily be tested by jumping the solenoid and applying power directly to the motor, my guess is it will run very well in both directions and operate correctly. This would confirm the burned, pitted, corroded, or improperly matching contacts in the down solenoid or it may indicate that the solenoid slug is not moving throught its full travel and prevents the contacts from making properly. A shot of lube between the coil and slug and a tap with a hammer handle can test for this fault.