The last 10% of the work takes the last 90% of the time, as they always say.
I'm hoping it's just a cracked solder joint- I think I can fix that without tearing the keyboard completely apart. If it's a broken switch or broken trace it's going to be a much more involved repair. A normal person would probably have thrown this keyboard out years ago- it's not a high-end board to begin with and it's known to have issues with keycaps breaking and lights dying. The lighting on mine is still good but it has very few original keycaps left. But I've grown used to it and will throw unreasonable amounts of time and money into keeping it working.