On my boat, a B36/2002, I don't have the barrel shaped port lights, but for the last five years I've used a rhin smear of "Vaselene" or petroleum jelly on the seal for each port light. Up to now it has been great success from a single annual smear of the stuff, and I've not had any leaks from them since then, though there were frequent leaks prior to its use. Just don't wipe away the grease every time you clean the windows.