Based on what you said, I think it is the control that has broken, especially if it is not moving properly and the motor is not even coming on to try and tilt the seat back. Perhaps you could test it by removing the control from both seats and connecting the functional seats control to that bad seat and see if it works. If not then it must be the motor.
There is no relay for the seat controls, and a fuse would affect both seats. Here is a diagram of the backrest motor and wiring. The relay and the bit with #2-7, is only if you have seat heaters. Best of luck!
Porscha
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