Rebuilding Rear Wiper motor

[vex]

I'll make this quick:
Rear wiper motor in the hatch never worked while I've had the car. Worked on it a little bit one day then when I closed the hatch it did one sweep before turning off again and never turning on. I've checked the power to the motor and it test strong and correct. I've tested the motor via resistance and it measured fine. I broke the motor apart and looked at the brushes and everything else to make sure it was mechanically sound. One bush seemed to have seen a spark or something as there's a little divot in it, while the other one seems perfectly acceptable.

I went ahead and ordered another used motor and i've tested it as well. The condition of it was unknown and seems to be in fair working order. No obvious malfunctions in the brushes. However it does look like it's seen some water seepage. It does not function even though it's getting power from the connection.

Any ideas on what I should do or check or how I can rebuild the original motor?