I have issues with the rear door on mine too- it definitely was not made as tough as the rest of the device. Mine is still holding on for the most part though. I don't know if you can get parts from Contour or not, but you should be able to get a dead on on eBay or something similar for a reasonable price and then scavenge whatever parts you may want. At least, that's probably what I would do.
As much as I love my Contour Roam, I think GoPro is the way to go if you consider purchasing a new camera. I have two GoPros and a Contour Roam. I love the GPS tracking, I prefer the shape of the unit, I love being able to use the Bluetooth without needing to snap on an extra piece (GoPros now have that feature built in, but mine are Hero2's) and I like the laser targeting system.
But the support, the software, the aftermarket accessories make me think GoPro is just the better option.