I just had my entire fuel filler tube replaced this past Friday 2-12-16 because the flap would not open to let the nozzle at the pump in to refuel.
The vehicle only has 3000 miles on it, purchased May 2015.
The dealer ordered the part, I had it in 2 days and they did the replacement ( under warranty ) I asked them if they dropped the fuel tank and they said they did not. I checked it out when I got home and it appears as if they pulled off the tire and the inner wheel well to get to it.
I figured it out by process of elimination ..
I had left my wheel lock socket in the glove box and it had been moved / used.
I noticed a scuff on the surface of my wheel where the lug nuts go
( that wasn't there 2 days prior when I had washed it )
I also noticed a rivet inserted into the mud flap that wasn't there before so obviously that's the way the got to it.
I immediately went to the gas station to fuel up and the flap worked great, only time will tell how many times it will fail.
I also had my dipstick replaced with the correct one
( also under warranty )