Yes, the deadlights on my Mirage look exactly like this. I like the sharpened putty knife approach. I must tackle this project soon.
Good winter job if you don't want to miss summer sailing!
When you get to it, maybe some of this will help:
Rebuilding aluminum frame portlites:
First step is to get the portlite off the deckhouse.
Then clean up frames and replace the seal for the plexiglas panes.
Probably best to cut new panes, perhaps slightly thicker unless you use spacers at inner side of frame.
Originally, a butyl rubber strip was used on the inside face of the frame, then the pane pushed into that. But it tended to soften in sun and oozed out! There were sometimes small spacers placed within the butyl to keep the outer spline tight, but more often the pane was not held as tightly and eventually leaked.
Once the pane is in place, the rubber spline is fitted. It doesn't go under the aluminum frame, it just fits into a groove in the frame. The frames with newly sealed panes are then fitted to deckhouse with sealant. Lifeseal would probably work. You want something that CAN be removed down the road.
Instead of the butyl rubber, I used 2-sided VHB mounting tape on inner face of frame - Kind of thing they sell at auto parts stores and even hardware stores for adhering trim or house numbers etc. I put strips of that in first in several places to act as spacers. I could only find it in large expensive rolls for size I wanted, but eventually found some from Hong Kong on eBay in shorter lengths.
Then applied a bead of 795 all around edge and pushed the pane into place (filling small gap around the edge between pane and frame). Once in place, I carefully created a bead something like the original rubber spline all the way around on the outside. I had first masked the panes to where I wanted the bead to end. Used wet finger to make a neat bead. Once set, used Xacto knife & straightedge to trim just inside the masking tape which was then removed. Wish I had kept pictures. Easier than it sounds!
If you took the removed portlites to a window shop that uses the 795 sealant, they may put in new panes for you at reasonable cost rather than buy more sealant and tape than you can use. It is used for windows in hi-rise construction, and even for windows in large aquariums.
The grey rubber spline is available for several makes of boats (Tanzer, CS, C&C) , but I found that they were all slightly different and before long fell out. Will never use splines again!
This video is install in a fibreglass deck frame, but I see he too also used vb
tape and 795.
One other thought. Some owners (including me) abandoned the original portlites and installed external plexiglas . These were held in place with a sealant (795 would be best) plus a number of through bolts or screws. Screw holes must be a bit oversize to allow for differential expansion otherwise cracking will occur. Something like this guy did, using 795 and oversize holes.