>>322419593
Update for those curious: after a few hours, the joystick stopped working in the X axis completely. It turned out that a couple of the solder joints were bad and had come loose. However, after taking the whole thing apart again and redoing the solder, checking with a multimeter, the joystick works again. Lesson is if you're really bad at soldering like me, check the connections before you put it back together.

Second problem is after taking the plastic joystick top off and on again so many times, it's physically lose on top of the metal joystick module; if I twist it around too much, then I can't actually get the full range of motion on the steamvr controller tester. I don't know the best way to fix this. I do have cyanoacrylate, but I know that's not the best space-filling option. The hole is only like 0.5mm in diameter, so I think I'll try wrapping the rod with a few layers of thin saran wrap. Will report back if it works.