Hi ... I can't help with the GS39, but I've owned a Gulfstar 37 for many years. All in all it's been a great boat. Assuming there is similarity between the 37 and 39, here's a few things we learned over the years:
- We did develop leaks into the cored deck through the bow cleats and stanchions. We used the West Systems approach, cleared out as much of the wet balsa as possible, and injected resin/filler. That stopped the leaks, until a few years later the next set of stanchions aft started leaking ... same drill.
- The boat (vintage 1977) had a pretty bad blistering problem by the early 1990's. We removed all the gelcoat and the outer layer of glass, ground out any visible blisters/wet spots, and again used the West System approach of a new epoxy barrier coat. The following year a handful of new blisters showed up when we scuff sanded the bottom paint ... we ground those, filled them and sealed with epoxy. Since then (10+ years), no blisters. It was a huge job ... if I had to do it over again I'd leave it to the boatyard.
Other than the above two issues, the only work on the boat has been "normal" maintenance. Let me know if I can be of any further help.