Power seat wiring
I'll attach a few pics of my relays just to verify your connections. These were taken before I cleaned everything up.
It sounds like you did a good bench test of the motor and I checked to make sure your connections were correct. If the motor runs in one direction, but does not reverse, that is very suspect of something wrong inside the motor. I would think that the motor would still respond in one direction when moved in the vertical direction when the switch is activated. At least it should click or try to move in the direction that the motor tests good.
Have you taken the seat switch apart and cleaned the contacts? I have found many seat problems are with the switch. I've cleaned several and they are still all working.
Since the motors are identical, you could swap motors and see what happens. That is assuming the seat is out of the car.
If you copy the pictures to your desktop, you can enlarge them for better clarity.
Good luck with it.