Its probably built up dirt/sweat/bodyfat sticking around the button, pull your controller apart and give it a clean, should be good as new
Try opening up the controller by unscrewing the back, tut here, then cleaning any gunk out with a damp cotton swab. You might want to do it for all the buttons to prevent future problems.
or i could b almost at breaking point have a good look at it and make sure its not rip if it is den u have 2 option replace it or get a new control.
take out the battery pack spray some window cleaner on the button keep pressing it and let it dry up see if that works just don't turn your control on until its completely dry or you can have a circuit burn
I just open it take the buttons and soak them in hot water than dry them off with a cloth. I take the plate and I shoot it with pressured hot water.
