I have hadd my J/30 for 4 years now and have basically sealed the windows each year with a little silicon. does the job but thought I might how I could do this more permanently and with a little better visual appeal.

You may want to consider taking the plastic portlights out completely and then re-bedding them in a different caulk. The last time I did this, I used a polysulphide/silicone blend. It worked ok, but it tends to attract dirt. So, I'm also looking for a better suggestion.

I re-sealed mine several years ago using Life Seal. It worked great. No problems and no leaks.

I remade and replaced my portlights about 4 years ago and used Life Seal as well. It is a combination of polyurethane/silicone and has not leaked yet. DO NOT USE POLYSULFIDE on the portlights because it will attack the portlight material and result in problematic leaks until they are replaced (experience speaking!) B. Cox

We made new portlights out of Bronze coloured plexi 3 years ago still not leaking.
1) Windows were fabricate 1/4 smaller than the opening flange.
2) Butyl tape was placed on fiberglass cabinhouse flange.
3) Windows were placed in.Mask around windows and gelcoat.
4) Fill space with high guality window installer silicone.
Products were purchased from a automotive window installer.
Plexi was purchased from a company call Cadillac Plastics.

Replaced my windows with new lexan about 7 years ago. Used GE Silcone II. Found that most good silcones will work. The secret to any good seal is to sand the two surfaces no matter if it is plastic, fiberglass, or metal. Use GoJo or another hand cleaner to clean up the excess silcone before it hardens.

Had a winch that I installed with silcone II and I needed to remove after about 4 years and I had to pry it off with putty knives and chisels. Could have used the winch without the bolts in it.