Tap-to-click works fine, and so does right-click - most of the time. Left click does not work at all, unless you press it very hard at the very corner and hold it there for a while until it registers, although it worked a little sporadically yesterday, worked completely normal the day before.
The computer was manufactured mid-2013, but the battery was in 2016 and replaced mid-2017 - that's all the modifications done to it.
I'm guessing it's a hardware problem, but the clicking sound and feel is completely normal.
Any ideas about what is at fault and how to fix it?