There are three places they can leak depending on the type of hatch. It can be the joint between the hatch and the fiberglass where it is installed. It can be where the opening part of the hatch seals to the rest of the hatch. This is a rubber gasket that can be replaced. The final would only pertain based on the type of hatch. These have a lexan piece that is siliconed into the hatch frame.
Each is a different kind of seal, but you can usually spray water and determine where the water is coming from. The hardest is to pull the hatch out of the fiberglass, then reseal it with the appropriate stuff. I'd guess 5200, but I'm not entirely sure. I'd only replace the leaky one and leave the rest. You could introduce a new leak!! I've never had to rebed a whole hatch and getting it out and cleaning the joint could be a pain depending on what is holding it in!
