I’m not sure how the device fastens to the wall, as BCS techs always did it. It may require access from inside via a panel in the “box” next to the passenger seat. Others here have repaired components by that route and can advise the best procedure, which may entail removing the seat for ease of access… hopefully not. There may be online videos that can help.
But getting the keypad unit entirely off the wall would to me seem the proper approach, so it can be opened to dry, and old sealant can be removed and new applied in a thorough manner. I personally prefer Lexel, but it can set up fast to the point it’s hard to work clean beads; so plan ahead, work quickly, and use a wet finger to form neat beads.
In my mind there are two parts, the outer escutcheon whose surround seal is obvious to the wall and can be old, porous, or otherwise faulty, and an inner keypad that may not be waterproofed to the escutcheon. That said, my thinking could be erroneous regarding the keypad mounting/seal; others here may know better. What I do know is that when the last tech, well over a decade ago, put ours back together with my request to super seal every possible water entry, the lock cycling ceased.
Joel