I have the same problem. I haven't taken the back off yet, but a few years ago I complained and the dealer told me it was not covered under my extended warranty. The service manager didn't agree with them and ordered some new fasteners and installed them for me at no charge. They lasted a year or two and now its back to popping off again. I called the parts department at the local dealer and asked about them and he said it was best to take the back off and bring a fastener in, because the ones the computer listed were pricey ($12 ea?) and he thought the body shop there may have a universal type fastener that would work and be cheaper.
It's something I don't think about often, but it really does change the comfort level of the seat. If you like your lumbar adjusted all the way out like I do, it feels like it isn't doing anything unless you shove the plastic back onto the seat again. I'm not super busy atm... maybe I'll go take the back off and see if I can get the new retainers.
These "Lego" cars are here to stay. It's great when all you're looking for is speed during assembly. But servicing snap-together parts makes it difficult not to break things, and the longevity seems to be reduced.
When was the last time you took a bolt off a car for the very first time and it broke? If it did, how often has that happened compared to these plastic clips breaking or becoming unusable?
Purchased these at Car Quest Auto store. Au-ve-co Products # AP 16695. GM Trim Panel Retainers. I had to modify the head a bit to fit the slots in the panel, but, they worked. Another possibility, that I didn’t try, is a GM Bumper Extension Cap Clip. Part #25639958. Both are 8mm diameter. If anyone tries, the later, let me know how they work. Hope this helps.