Here's an update.

It's not completely dead, but there's definitely a dead component inside the RF module.

I have an ancient "signal tracer", effectively a high-impedance audio amplifier, which can be used to probe circuitry to see where a signal exists and where it doesn't.

Here's a block diagram (and pin-out) for the RF Module in the factory tuner.
Note that pin-1 is nearest the Antenna Jack.

The FM audio is working at the Level pin, but not working at the RDS MPX pin, nor at the FM MPX pin. This indicates a faulty FM Demod stage inside the RF Module.

Next I'll pop off the cover and probe inside the RF Module, to see if the FM Demod is accessible and repairable.

-m