I asked because on the matter of the gasket, there are threads here that recommend taking the fixed port lights to an auto shop for gasket replacement. The idea being that the gasket is a common auto part, and they can do it easily. I can't find the thread at the moment, but it's worth searching (and confirming my memory) for if gasket is an issue.
I like LIfe Calk myself for port bedding, and to me it's even easier than butyl tape. Butyl tape oozes for a long time, and I regret using it for large surfaces and now confine it to smaller things like deck hardware, screws and so on.
Here is Maine Sail on the topic of bedding ports, from another thread:
Consider the future. Nothing is permanent on a boat so when an item also has a mechanical seal I look for the lowest possible adhesion & longest flexible life. 3M 101 or butyl would be my choices. Polysulfide handles UV better than polyurethane and the jury is still out on polyethers like UV 4000. I have had UV 4000 yellow in one season.
Some like Life Calk which is another polysulfide but I personally have not found it to not hold up quite as well as 3M 101.
3M UV 4000 = 300 PSI per sq inch adhesion (polyether)
3M 4200 = 300 PSI per sq inch adhesion (polyurethane)
3M 101 = 139 PSI per sq inch adhesion (polysulfide)
Butyl Tape = 10-20 PSI per sq inch adhesion (butyl rubber)
Originally Posted by Lyle
The March 2009 Sail Magazine on page 61 recommended for lexan professional glass bedding products:
GE Silpruf SCS2000
Dow 795 Silicone Building Sealant
Not just sail magazine that recommends those products. I believe they consulted Tony D'Andrea of Select Plastics who owns the worlds largest hatch repair & warranty facility.
Dow 795 is the most widely used product for bedding cast acrylic, what should be used in most marine applications, and polycarbonate/Lexan, what should not be used in most marine applications.
This however is not what should generally be used for sealing aluminum port frames to gelcoat. The 795 or GE SilPruf are used for direct bonding of acrylic or polycarbonate directly to gelcoat or directly to a frame then the frames are sealed with something else.
Some port manufacturers such as Bomon, not to be confused with Bomar, use neoprene foam weather stripping to make the seal. These neoprene gaskets have very little, if any, "bond" or PSI strength yet stay dry for a long time. New Found Metals recommends butyl too..
This is not to say you can't use a silicone for a frame to hull bond but future repairs will become very difficult due to silicone contamination and the next bond may not bond at all..