If tightening the dog does not cure the leak, and the gasket seems to be OK, have a look at the horizontal gap between the upper and lower frame sections on the outside. This is sealed with some sort of elastomer sealant
, and eventually it looses its grip and, despite looking ok, admits water
. Check to see if it is still bonded on both sides of the gap.
The cure is pretty simple: using a razor blade or other thin and sharp edge, remove all the sealant
that you can reach (from the outside). Be sure that the surfaces are clean and free of debris, then degrease with some acetone or similar solvent. I often use a feeler gauge to work the solvent into the crack. Then mask off the area carefully, just at the edge of the crack, followed by forcing Sikaflex 291 or similar sealant into the crack. Use as much pressure as you can to get the goo well into the crack. When you are happy with this, dress the seam with a finger dipped in turps, and then pull the tape before the goo sets up.
I was instructed in this procedure by a pro in the portlight and hatch refurb
business, and have done it a number of times, all quite successful. Incidentally, the pro strongly advised against trying to replace the main gaskets. He said that even after years of practice he found it very difficult to get the new gasket (which is not something you can get at Clark Rubber etc, but a proprietary shape owned by Lewmar) to fit into the extrusion, so be warned!
Good luck with it!