Finally was able to drop the car off for a day at the dealer. I picked a day when it was supposed to get cold overnight. I typed up a note explaining the history, the suggestions from the forum, etc. The service manager had left for the night when I got there, but I wanted to leave it there outside for the night anyway.
Next morning, I did not hear from them first thing, like I usually do. I finally called around 10:30AM, and they said they were looking at it at that time. It was already getting warm.
Of course, by the time they got to my vehicle, the radio was working. "Unable to verify complaint." Like I am a moron who does not know how to turn on a radio???? "No fault codes," as I told them. "No TSB's".
Dealership "tightened up the wiring harnesses" and installed two software updates: 08-016-11 and 08-008-12. I am not sure what they were supposed to fix. But a couple of days later, when the temperature dropped again -- no radio. Again.
So apparently there is no fix for this problem, or else I need to go to special training to learn how to operate my radio.