The switch with the push button that engages with the black rod is shown here. One of the brush connections can also be seen in the background in this picture.

The heatsink is clear. I unscrewed the copper plate and found some white heatsink compound below against what may have been an aluminium plate

I had not encountered a heatsink built into a switch before, so I tried to take the switch apart. I could remove the top cover, but the flexible dome resisted all attempts to remove it, but it is possible to see a circuit board inside. The fuzzy pictures through the crack were taken with a boroscope.

The switch seemed to be open circuit on the neutral side, so I looked for replacements. This was before I realised that it was an active circuit. The only candidates that I found seemed to be ordinary passive components..