The more I think about this the longer a shot it appears likely to be, but
here goes anyway:

I have a car radio with button switches that don't work. Buttons for bands,
memories, that sort of thing.

The switches are a plastic button, a printed circuit with two traces, and a
kind of black rubber doughnut with a tit in the middle. The tit sticks out
a bit more from the bottom of the assemble, so it hits one pc board trace,
the joint between the tit and the ring flexes, then the ring hits the other
pc trace, and the switch is closed.

Many of these little rubber things have broken where the tit is joined to
the dougnut. I'm off to another car radio repair place tomorrow - at the
really good electronics place that I go to first the guy just shook his
head, so I don't have much hope of finding new bits. This radio is old and
foreign.

Is there a conductive flexible rubber glue?