In the past, I would "fix" it with some 3M 5200 to seal the cracks and screw hole. This would generally stop it from leaking for a couple years and I would repeat the process. Last fall I went to apply some 3M 5200 to the cracks on the rear hatch rim and found that the crack had grown considerably since the last time. Also, now, the front hatch rim is cracked as well.
I had great luck reattaching the front hatch rim on my 1996 Romany Explorer a couple years ago when it just came loose. It was then only held on by rivets, which don't make a particularly waterproof seal. Apparently someone has reattached or replaced the hatch rim in the past and didn't glue it very well.
I reread the very helpful set of articles on this process by Sherri of sherrikayaks.com (starting with Part 1), and started on the process that she describes. Things didn't seem to work as well for me, or I am more impatient. I won't describe the whole process since she did such a nice job, but I will show some pictures and discuss how I did things differently than she did.
When I got to Step 5 of Sherri's approach, prying off the old hatch rim, things weren't moving and I felt that the fiberglass was flexing too much and the glue wasn't giving at all. I was afraid that I was heating things too much, since the fiberglass was flexing easier, so I looked for a different approach.
I used a carpet knife (that I happened to have in my tool box) to cut the glue around the outside of the hatch rim, getting as far under as I could without risking damage to the gelcoat.
I also used that knife to cut the glue around the lip of the hatch rim on the inside of the hatch.
Then I had to attack the rim itself. I used the Dremel tool with a cutting disk to cut through a section of the plate of the hatch rim which was in contact with the gelcoat. Being careful to only cut through the plastic of the hatch rim. It took several times to get the right depth. The glue should be somewhat thick and you only want to cut just into the glue. I also cut off the inside lip of the hatch rim in the same location so that I could slide my carpet knife under the hatch rim and cut the glue bond. After I removed the cut away section, I had this:
Then I could work my way around the hatch rim prying with a screw driver and cutting the glue bond with the carpet knife. At this point I didn't use the heat gun any more.
I would break off pieces as things got in the way. Or they would usually break off on their own. In the end, the two hatch rims looked like this, lots of carnage.
Once all the pieces of the hatch rim had been removed, I just had glue left from the old application.
Like Sherri, I cleaned the old glue up with a wire brush in the Dremel tool, working very carefully not to damage the gelcoat.
I had to add some fiberglass to the inside of the hatch to reinforce and fill the screw holes since the fiberglass there was was also cracked and I had no intention of leaving the holes in place or using screws with the new hatch rim.
I masked off the deck to keep from getting stray adhesive where I didn't want it.
I cleaned the gelcoat with acetone and the new hatch rim with isopropyl alcohol. I then applied a thick bead of adhesive to the hatch rim recess and carefully positioned the new hatch rim and twisted it while applying even moderate pressure to seat it in the adhesive. And cleaned up any adhesive that oozed out on the inside.
For this repair I used Sikaflex 221 and 10" hatch rims from Sea-lect Designs. I am in the process of letting things sit for a few days to cure before I see how well things worked out, but I have no concerns at this time.
When I did the hatch rim reattachment on my Romany Explorer, I used 3M 4200 since it was locally available. That hatch has been completely dry for 2 years now.
