Acer ES1-132 Touchpad bottom left and right button not working

[starLED]

Acer ES1-132 Touchpad bottom left and right button (that can be clicked, not tapped) are not detected in Windows or Linux (tried both to exclude driver issue). Moving the mouse and tapping is working fine.

I have disassembled the touchpad, but I am puzzled how it actually works.

There is a clickable button in the bottom middle of the assembly, and when you press bottom left/right on touchpad it actually just clicks that one middle button.
How does touchpad actually detects left/right button?
And how to diagnose the issue? It seems there is some overcoat on the button, and multimeter leads can't show continuity.

 

[Tony Stewart]

I suspect there is a detent in the corner is a drop in DC resistance while the touch sense I believe is a rise in capacitance or drop in AC impedance.

Be careful not to create more failures.