I have no personal experience (yet) with the ones on these G-Bodies, but if it is anything like I'm picturing from my 15yrs of working on other cars you'll have 2 options:
1. Replace them (we all know the options here - and considering how nice your cars are, might not be an option. On newer cars, this is the path of least resistance)
2. Carefully clean off the remains of the tape from the molding. Then get some 3M double-sided tape (this is what I'm pretty sure you're talking about is on the molding) and reapply in the same spot. Make sure to get their preparation adhesive swabs, has been the difference between the tape sticking and falling off on multiple things we've used the stuff on.
If it is literally a thicker layer of a foam (say, 1/8" or thicker) 3M makes this stuff too and it goes along pretty much the same process as my #2 above , just generally that stuff isn't as "sticky" as the double-sided tape. This stuff is generally used where you're going to bolt a window down or something, and it gets squished a little.
Hopefully this helps a little, or gets the wheel turning.