On Sun, 13 Oct 2019 02:19:33 +0100, J. P. Gilliver (John) wrote:

It _may_ be possible to dismantle and repair the switches themselves,
but I'd not like to try.

Usenet is a community potluck where everyone chips in where they can.

I didn't read all the details in the thread, where my value add is that
o I can simply vouch for fixing mice by taking them apart (carefully).

My suggestion to the OP is to take the mouse apart, like I did he
https://i.postimg.cc/v83WFn2v/mouse01.jpg

And then clean everything up and look for something broken:
https://i.postimg.cc/5tr2SxsL/mouse02.jpg

If nothing else, it's useful to see how the thing works inside.