We are new owners of a 1998 36mkII. Our boat was previously a charter boat. There were a few leaks in the hatches. We were not successful in our first attempt at repairing the leak in the escape hatch in the aft cabin. Is there a preferred marine sealant?When we repaired the hatch we noticed the window box was not flat. Several washers had been used to level the window. We sealed with mono exterior sealer and tightened down. Hatch cover would not sit properly so we had to loosen the screws. Did it a little too late and the sealant didn't stretch and lifted off the frame making the leak worse than ever. Any advice regarding materials and methods for fixing window/hatch leaks would be appreciated.