2BEFORE removing the rotor assembly, inspect for corrosion or water damage. If present, take the motor to an auto electrician. A DIY repair is viable but will require some experience in electric motors.
This winch appears to have had little use, so the key areas to inspect are the copper connections on the terminals, and the bearings. The solder connection on these posts can fatigue, causing poor contact and therefore winch failure.
The bearings on either end of the rotor assembly are also simple to inspect, and replacement bearings can often be sourced cheaply from a local bearing supplier.