I'd ask them for clarification. You can be very blunt with them: What part is inoperable on my car, and what is the Nissan part number of that part that you wish me to spend $7500 to replace.
If they won't answer you, time to speak to the service manager.
If the "passenger seat adjuster assembly" is functioning, they need to tell you specifically which part they believe to be nonfunctional.
Let us know what you learn!