I learned that back in 1984, my first new car, s-10 blazer. Same dealership location, different owner. Same crappy service over the years. I brought the s-10 in because when I wiggled the volume knob on the radio, BOTH front and rear right speakers would cut out. Very repeatable. Simple right? First trip they changed one speaker. Next trip they changed the other, then finally the radio. Other headaches over the years too like you say, screws left out, etc. I like GM cars, but hate the local service. Over the years, if a warranty problem came up, I'd fix it myself if it was under $50. There is no limit to what they can screw up.I do not trust dealer service further then I can throw them.