I thought I'd have a go at the horn push next and dragged it out of storage.  The first thing that I noticed was that the lever was very rusty.  Then when I fitted it altogether I was worried about how badly the aluminium ring turned on the bakelite horn push before I realised that a few parts in the bag looked like they should be inside the unit.  So I took it all apart.

I was careful to take some photos on the strip down.

I think this would have been chrome plated back in the day, it's going to be black from here on in.

The lever took the paint well but the button didn't which is a shame.

So tomorrow I need to remove the wires from the ring connectors and solder them onto the new wires before refitting it all.  I do need to do something about the bakelite as it looks very dull.  Apparently it is best to cover the surface with black ink before polishing with shoe polish.  I don't have black ink, damn.