Those switches are mild steel inside and corrode away in the salt air. I took mine to pieces and it was just full of rust. They were no longer available in 2010 and it is now 2024!
The best thing is to buy an IP65 box and screw it to the electrical panel behind the switch panel. Inside that put an new RCD and reroute the wiring. Keep the old RCD obn the switch panel just to make the panel look complete.