The large portlights in the main salon are a royal pain to replace/repair. The glass is curved to match the sides of the cabin top so it is difficult to find a drop in replacement. The frame is pretty cheap and will bed easily when removed. Especially if a PO got a little crazy with the sealant to try and stop leaks.
My plan for this fall is to try and remove the entire portlight without damaging the frame and replace the glazing around the glass. Then I will rebed the frame with Butyl tape.
For a short term fix I have had good luck with using the blue painters tape to cover the frame to cabin joint and to cover the exterior glazing. It is not pretty but it will buy you some time while trying to find parts or come up with a permanent solution. I suggest changing the tape every few weeks.