I had an issue with a new 1985 Z-28 some years ago. The 4WDB's were less than adequate when purchased IMO. I had taken it in for small warranty services and asked them on three occasions to check them. Each time is was "could not duplicate on the service ticket. The warranty ran out about a month after my last visit and had to take it back for warranty rework. I again complained about the brakes. Well, low and behold, this time they determined the rear calipers were sticking and gave me a quote to repair. They had records as well as O had receipts of each time complained about the brakes while still under warranty. My dad was a life long body shop owner and told me to keep my cool and tell them that I wanted to speak to the GM Regional District Manager. The service manager disappeared for a few minutes, came back and told me they would replace the calipers free of charge.