the source of your leak is likely the "G" gasket. When I got my 320 6
years ago, every portlight leaked, and leaked badly. I replaced all the
rubber gaskets. Yes, they are a real PITA to replace. All still leaked.
I then replace the O rings in all the dog ears. All still leaked. I then
read about the G gasket on our list, looked closely at mine, and yup, dry
rotted. Given your hull number, I'd guess yours are dry rotted too.
I had perfect success with fixing without rebedding the hatch.
On each portlight, horizontal, mid section, visible on the outside (deck
side) of the hatch, is a seam, filled with a gray gasket. I would guess if
you inspect closely, you'll find that dry rotted. What I did is take thin
needle nose plier, and a pick, and pulled that seam portion of the gasket
out (this is the g gasket, if you are able to extract a whole portion out
without tearing, you'll see why it's called a g gasket). It should come
out fairly easily, with minimal need for cleaning the surface afterwards.
Then, after you've removed the g gasket, on the outside (deskside) cleanly
take off the aluminum along that seam, and where it meets your fiberglass.
Then, with this Dow Corning sealant:
From the outside thickly fill in gap. Then, with the back of a spoon,
smooth the sealant flat (why you need the tape off your frame and
fiberglass). Then, apply another squirt on the inside of the frame (this
is a little harder to reach with the sealant nozzle, and unfortunately
harder if you have your rubber gasket for the lens in, but can be done;
fortunately on the inside, doesn't have to be as clean, it's hidden well).
Let cure. Come back with a razor blade, very lightly score the sealant
along your taped area, and then remove the tape and the excess sealant on
the tape should cleanly break.
I have not had one single drop leak since I did this. It was the source of
ALL my leaks. And this is actually easier to do than replacing that rubber
lens gasket. I did all 7 of my portlights in about 4 hours. Don't cheat
and get another sealant. You want that Dow Coring sealant I recommended.
Its used to hold windows in skyscrapers. It's the real deal, works great,
bonds well, and breaks along light scoring for a nice clean up. You could
never tell I did the job it was so clean (except for my first frame where I
hadn't taped, and then realized I needed to tape for this sealant).
Hope this helps, happy to answer any questions.
-Christian Caperton 1994 C320 #138 "Canuck" Monroe Harbor, Chicago, IL