You've had water in the motor. The two black things are brushes. Pull them out and sand them until they're smooth. If they're stuck try pushing them down to break them loose. Same for the other two. They also need to float freely without binding in their sockets. The spring below them keeps them in contact with the commutator, which also needs to be sanded with a numerically high grit paper to remove the oxidation. You should see a bright metal finish when you're done. You want the surfaces to be as clean and smooth as possible. Spray everything off with CRC electrical cleaner or similar to remove the sanding and brush residue. Apply a little grease to the bearings and silicone where the housing meets the ends of the motor. You should be good to go after that.
Warranty and customer service won't matter if your equipment fails during a zombie attack.
Torture numbers long enough and they'll tell you what you want to hear.
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