Had to replace the parking brake mechanism after the button popped off. It’s a pretty common occurrence and unfortunately you have to replace the entire unit for $60-70. It only takes about 20-30 minutes to do it yourself and save several hundred dollars taking it in if you’re out of warranty.
http://www.ecstuning.com/ES168663/ ($51 – without auto-park button)
http://www.ecstuning.com/ES207256/ ($48 – with auto-park button)