You can remove the motor first to check the condition of brushes and armature. Usually brushes are worn out and this warrants replacement. As for the armature if there is a deep groove already better replace the whole
Samurai motor is a rarity in my part of the woods, was able to get a suitable replacement from a suzuki carry wiper motor, although had to rewire the motor by using the correct color code on wiring,
Works great now, 3 speed and strong enough.