The lock cap fell off my driver side door a few weeks ago, and because of that, the door handle slid. I took it in to get it replaced, fortunately they had one one in stock, so it must be common enough to stock that part. After I left the dealership, I was at the store and when I returned to the car, the new cap fell off. I had a feeling something wasn't right because the door pull seemed a little tight like it was caught on something. So I went back to the dealership directly afterwards and told the advisor what happened.
We walked to my car and I saw how he fixed it. Apparently the person who put it on the first time didn't seat it hard enough. He said the sole purpose of that cap was to keep the handle from sliding, but I had to inform him that the key fob bluetooth chip is in that cap as well. My door wouldn't open anymore by just putting my hand behind the handle and you could see a little chip inside the cap.
To put on the cap, pull on the door handle then put on the cap. You need to keep the door handle out and push on the cap with a lot of pressure so that it snaps on. I couldn't tell if he had attach it to something first before pushing. I just saw him place it on and had to use a lot of force to get it to snap on. I think it took him 30 seconds total to fix it. It was really that simple. It cost me about $75, but you can buy them online for about $50 USD and do it yourself.