I think I may have found the issue but I want to double check. Whenever a pair of headphones is plugged in, are all three of these pins on the jack suppose to look separated like in the image?
I wasn't getting anything through the left channel after reflowing parts of the alps pot, but while listening I poked the very top pin in the headphone jack so it would touch the plate across from it. It was separated like the other two pins, but not as wide as them as you can see in the image. I got audio in both channels whenever this happened, and the pin went back to being separated like it was before after poking it. The audio remained in both channels so I ran a left/right channel test from youtube through the amp to make sure it wasn't the right channel coming in through both channels. It's definitely working now, but the top pin on the jack concerns me. If I pull a little bit on it to separate it more I lose the left channel completely.