Ask the dealer what, if any, discount they'll put on the trade if you don't fix it, but I'd just trade in the car, if you are doing so at the same dealer that you are buying the 2015. No sense in going through the inconvience of dropping the car off and picking it up. In 2002, I weighed fixing the right, rear fender of my '98 when trading it (scrapped a cement support column in my work garage three days before deciding on gettng a new one), but the dealer didn't put that huge of a discount on it with the war paint, so I never got it fixed. Your dealer should give you a trade-in value that should be good for a week or so, with a limit on new miles (no cross-country roadtrip, for instance). You can then decide if the fix is worth it (DIY or Indy Shop), or even test the private sale route, quickly. The fix could be an easy, relatively inexpensive switch problem or a more involved, expensive, new regulator inside the door.