[Mike Kelly]

Strange.

Each time you remove the switch: Is there any indication of the fluid squirting out the hole under slight pressure ?

Maybe you can get somebody to press the brake pedal slightly with the switch removed just to get an idea of what is going on at the switch port/hole. With the pedal fully up, there should not be enough fluid pressure to activate the switch,

Another idea , remove the switch and test the switch on the bench with a battery and two wires , poke something down the hole while the battery is connected and see how sensitive the on/off mechanism is. It's probably a rubber diaphram or similar ?