I sent a customer's 245 Grady White to the dealer to have its annual service. They called me and said that they found the Bennett trim tabs to be severely corroded with some holes right through the SS trim planes. Sure enough, when I went to check it out, along the front of the tabs closer to the hinges, they were rotten. As well the hinges and backing plates were also severely pitted. The zincs on the tabs were still functioning but due for replacement. This boat lives all year in saltwater at their private island. There is no hydro to the dock and no metallic structures in the area. When tied up, the outboards are tilted up out of the water with the battery switches off. There is no other metal in the vicinity. The only possible cause that we can see is that the trim tabs were installed on top of an existing layer of bottom paint. They are going to sand off this paint and leave a 1/2" border of bare gel coat around the tabs to provide isolation from any galvanic activity. Any other thoughts as to why this happened? We want to correct the cause before putting the baot back in the water. Thanks for your suggestions.