Electric motors are pretty simple and sturdy; the armature and magnets would likely clean up OK. The weak points that would be questionable are the commutator and the brushes and brush holders and springs. The commutator must be smooth clean copper everywhere, or the brushes won't have good contact. At least the copper on the commutator won't have rusted; it may still be OK underneath all that crud. But if the copper has been mechanically abraded off, the commutator would be toast. Looks like that winch has been thoroughly submerged in water.
Certainly it would be a lot easier just to replace the motor, and easier peace of mind, unless you are very thrifty or just want a project. Last time I bought a new Warn (9.5XP) motor, it was $300 dollars or more - don't remember exactly.