Hi Blaster,
We have a 1993 Hunter Legend 35.5. I think you're talking about the shower sink that sits on the fiberglass panel ledge in the shower area. We have the same setup. I believe that the whole fiberglass panel is just siliconed in place around the edges on that starboard wall as there are no visible fasteners. My guess (I haven't needed to get inside there yet) is that you would need to carefully cut into the silicone around the edges to remove that panel and gain access to what is behind there. I think it's worth a call to the factory to inquire. Marlow-Hunter factory phone number is (386) 462-3077. Good luck!