What version PCB? because there are quite a few of them.
If the Daughter board isn't damaged, and the connection between it and the main board is good, all that's really left is the solder joint on the MCU for that button.
Pretty odd for only one button to fail, as I've seen some of these things that are in just wretched shape from years upon years of use and abuse, and after putting them back together they still work.