With six ports on the cabin top, this was a major refit job.
After removing the internal compression ring in cabin, each port required a good scraping/cleaning to remove the goop used in 1977 to seal the glass ports into place.
Utilizing silicone and experience, 4 out 6 are still dry today.
The two larger main cabin ports both leak less that a year after refit.
Ahhh, the joys of boat ownership.