I've heard of this situation before, don't recall where
If I had to hazard a guess, ok I will..
1st, the Keypad.. It never works? I'm thinking the seal around that part of the door may be defective allowing the moisture into the Lock Assembly.
The typical Door Pin Switches were replaced by Micro Switches mounted to the Lock Assembly. You can see what I'm getting at here..
If the Keypad was moistened from the business side, it too may have been killed.
Removing the Door Panels and close inspection of the Lock Assembly is the only way to test my theory.