Replace with Bomar Hatch
Check out West Marine Bomar low profile 20-1/4"x20-1/4" mode l117871 in aluminum.Carefully break the old sealant with a putty knife, & clean up the opening with acetone. Fill the old screw holes with Marinetex and carefully pre-drill for new fastener locations.Use an electric sander on the vertical edge of the deck to true-up or enlarge the opening if necessary, and seal deck edge with west system if the plywood is showing or the gel coat has delaminated from the plywood. Cure as needed. Install with two liberal strips of Life Seal Sealant on the deck surface (verify Bomar instructions for compatibility). Install screws loosely until sealant oozes out uniformly at flange but don't tighten down and squeeze out all the sealant. Clean up the extra sealant as you go and final tighten the screws in several hours. Seal between the inside flange and the edge of the liner with the same sealant from the inside. Cleaning your hands several times helps keep the sealant off everything else. Good Luck.