Longitudinal seat repair - passenger side for 98 328I convertible

What is your question?

Seat does not move forward or back on the passenger side. I fixed the gear that was not working on the seat recline, but can't find anything on the longitudinal repair. Would like to just replace the gear box if possible. I was at the dealership today and inquired about it and they advised it was about a $600 repair. I asked the technician it is coule be fixed if I had the part and he said yes. Can you help guide me on what it would take, how to and where to get the parts? Thanks!

What makes this problem better or worse?

It doesn't work at all, had to put it in so I could put the seat back in the car.

How long has your 1998 BMW 328i had this problem?

2 years