The dealership looked at my radio which had recently refused to release a cd.
They disconnected the power, reconnected it, and the cd ejected automatically.
So it appears at least at a first approximation that the problem is with the eject switch itself, which is what they said it is. Of course it could be a deeper error in the circuitry, but there is no real way to know.
Is replacing the switch itself something that can be done easily?