L2 trigger activates by itself

Bought a PS4 controller second hand. The L2 trigger button keeps activating by itself as if being constantly repeatedly pressed. As the seller won’t pay me back I have been trying to fix it.

So far I have tried:

Replacing the L2 trigger button, spring and rubber part under the button.

Cleaning the interface under the rubber part on both sides with isopropyl alcohol.

None of the above has solved the problem and it happens even when the buttons and rubber part are removed.

Any ideas on how to fix it?