ok, so it's this one:
https://www.ifixit.com/Teardown/MacB...+Teardown/4990
Notice how the battery is directly below the trackpad? If it swells, it will stop the trackpad from clicking. You said when you press down on the trackpad, it's hard to get it to physically click, right? You can still tap it or maybe force it to click in some spots.
could be swol'd battery. You can just unscrew the bottom and take a look at the battery in that model. Is usually obvious if it's swollen.
---------- Post added at 04:23 PM ---------- Previous post was at 04:21 PM ----------
If the battery is swol'd you can replace it hella easy. If the trackpad is actually bad, that requires more work. Not hard just lots of screws and cables to carefully remove and replace.
https://www.ifixit.com/Guide/MacBook...lacement/12661