There are a lot of different wheel weight shapes that allow the weight to fit snug up against the wheel lip. If the shop doesn't have the right weight they will normally use what they have that is closest to what's needed. Then a few miles later, they fly off. I've seen some places use pre-enjoyed wheel weights, and those don't last long either. Try a GM dealer, and ask them ahead of time if they carry the weights specific to your wheels. They will usually say "Yes, we have them.", but make sure they check first. In the '90s when I worked at a GM dealer we had 6 different boxes of coated wheel weights depending on what car we were working on. Hope this helps.