Before and after shots as requested.
The washer on the rod, shorts the two contacts in the lid to give the low fluid indication.
The rod only moves a couple of mm when retained by the cap.
You have got the same comedy brake fluid sensor cap as I had.
There is a plastic cap that fits over the rod and limits the travel.
This seems to ping off over time.
I made a new one from a cap I found in my plumbing box.
It needs to be sealed to protect the brake fluid and the contacts on the sensor.
Cheers Pete