GM seems to have cheaped out on some of the adhesives they use. My coupe had a recall noted even before it was sold - they had to reglue the inner liner in the roof panel so it wouldn't come unglued in service and settle on the driver like a great bat.
I'd have thought that all the adhesives etc. would have been stuff they had tested and had been using for years, but maybe bot......
Another vote for 3m Window Weld. My Sky's rear window started to break free last month. I checked this forum and watched some Youtube videos on convertible window glass replacement to get the basics. I then order the Window weld ( 3M Part # 08609 About $22.00 a tube). Just be sure to also order the primer (3M Part # 08682 about $25.00 for a "small" bottle- Cost than the Window Weld- Go Figure), In addition, you will need suction cup style clamps to hold the window in place while the adhesive dries. I used the Sealey brand clamps but others are available (Sealey Part # RE006 - about $40.00 for 6). All available on Amazon. I was lucky and only a portion of my window came loose so I only needed to use two clamps however due to the small size of the Sky's rear window you may need to do the job in stages because the window glass is too small for all of the clamps you will need. Dry fit/clamp to determine how much you can do at one time. The adhesive is a messy black goop consistency so wear gloves and use a smaller amount than you think you will need (the clamps will squeeze out a lot of the adhesive). Don't clamp too tight and wait until it dries before trimming the excess off the glass. Use a razor blade with a putty knife as a barrier between the glass and your top so the razor blade doesn't cut the canvass material edge when trimming off the dried adhesive. Last piece of advise- Plan ahead and don't rush.
Yes, I did that repair using the 3m myself. My glass was not completely detached, but it was getting worse by the day! I did not use any primer, just cleaned the entire area well especially where you plan on glueing the glass. It was not an easy job, but not extremely difficult either. I would suggest taping off the glass of the window where it meets the ragtop before hand and using some kind of syringe to push the glue between the glass and the ragtop. That adhesive is black and viscous. If you do a sloppy job, you will pay hell getting that adhesive off either suface ?