You did not actually say whether the leak is against the rubber seal of the window itself, or if the entire port light installation is leaking, as dL has assumed based on what your report/inquiry implies. We may assume the latter, but different solutions would apply depending. BTW, I think you mean “caulk.”We have had a lot of rain over the past week. In our aft room, above our bed, the port window that is below the seating, has a small drip leak. Anyone have an idea if 4000UV would do the trick and do you cock the outside/inside or just the outside? I'm not even sure why there is a window there considering you are just staring at the seat of the cockpit.