Cold temperatures, audio issue: won't turn on

Over the winter months, when the temperature dropped down into the twenties or below, the audio did not turn on. When the cabin temperature warmed up, the unit could be activated. I suspect some kind of a sticky issue -- like grease or such -- that might not flow, but that's just a wild guess. What might it be? How to fix it?

This is the standard, non-JBL, audio for the Prius. Once warmed up, no complaints. Now, it springtime, it starts when button pressed.

Suggestions? And, if they include such things as spraying a mist or oiling ... how do I get into the unit?