Welcome to the Board Willie. Thanks for keeping another Helms on the water.
Yes common to these and all fixed aluminum ports of that era. I understand you can get gasketing from your local well supplied RV dealer. They used the same type of windows back in the day. I have not done a search on Google for them in awhile, but I'm sure there is info there also.
When I fixed mine, I didn't go the gasket route. I carefully removed the frame from the boat and cleaned out the track and took one of them to my local glass shop. He recommended setting them in glass sealing silicone caulk for a very long lasting job. Glass companies use a special formulated silicone used in commercial glass like you see on high rise buildings. You can buy a tube from them or search 3M for their product. I had the glass shop replace the glass and seal it as he recommended for that window. Cost me $35. I must add that the previous owner had replaced the original plexiglass with tinted safety glass and I cracked the glass when removing the frame. I think he set the frame with 3M 5200 and was a bear to remove. Don't doo that! Ended up using DeBond after I cracked the class. good stuff.
Bottom line is I thought I could do a better job than the glass shop and did the other window on that side myself. Still need to do the Port side.
Also, since you'll be doing a lot of other work on the boat, here is a link to how the jobs are done best. Need Butyl Tape ?? Photo Gallery by Compass Marine at pbase.com
That link is for Butyl tape, but look at the "All Gallaries" and click the how to section for finding out the correct way to do stuff. He has how to replace Ports in there.
Ask away on any other question that come up.