Starbrite waterproofing agent. Clean the top or canvas, make sure it is bone dry. I take a 3/8" nap synthetic roller and roll a decently thick coat on the top and use a chipping brush on the side. You're better off doing 2 thinner coats (allowing it to dry a few hours in between).
Really the linseed oil and all that is a bandaid on an old boat. After 10-15 years the Butyl or sealant that was used to bed/seal the windows has dried out, shrunk, and failed and that is mainly why it is leaking. Really the proper way to fix it is to pull them and re-seal.
Good luck, resetting should solve the problem. Nagged me for two years on and off till it got real bad last winter with the freezing. Then it really opened up.
I think the glass itself is tinted, but I don' know that for sure. I still suggest a low heat. Tape some shrink wrap material over the windows so more water or snow doesn't leak in while you are drying and applying. This is more than a one day process I agree with Capt J that the gold standard fix is to re-bed. Which I was and am prepared to do if the linseed didn't work. But as I've said, big surprise to me - it worked!
Great thread. I have a similar issue, and it seems the exterior caulk is deteriorating. When washed it leaves streaks. I get some moisture inside, and may try the linseed, but is it worth trying to remove the old exterior seal and replacing, or is that too big a job?
Capt J is correct. Egg Harbor had the same design windows that would also leak. I pulled my windows, cleaned up all the old sealant, coated the wood with penetrating epoxy, and then re-bedded the windows. Problem solved.
If the outside gasket has deteriorated I don't think the linseed oil would help. The idea was to apply it to the dried wood to re expand it so it provided some hydraulic pressure outward
If it's Sikaflex you have on the exterior, that stuff always bleeds after a few years. Sam's marine parts sells a rubbery primer you can paint right on it to seal it. I forget what you mix with it to thin it, acetone or something, but mix small batches as it thickens pretty quick and tape the area's you don't want to paint, so you can just zip down the caulking with a thin brush.