Not a question - This one is to help others!
I have been having issues as of late (over a year now, but its a short time considering the computer is 9 years old). My trackpad and keyboard were working intermittently, and the element that usually made them stop working was any type of physical stress on the trackpad or the frame.
Long story short, I troubleshot the issue down to the PCB underneath the trackpad being damaged by (Apple will never admit this...) a bulging battery. I was able to almost systematically be able to reproduce the issue with the battery out, by pressing at the proper place underneath the trackpad with the battery out.
Now you have two options to resolve this issue.
1 - try to find a decent (or brand new?) top case -- IFixIt is out of stock permanently -- and replace yours, AND THE BATTERY!
OR my fix (not for the faint of heart)
2 - Remove the gray plastic cover from underneath the trackpad (unplug the computer!! ), and with the finest tip soldering pen you can find, touch up the welds that you are comfortable touching, because my guess is the bulging battery causes some welds to micro fracture. THEN CHANGE THE BATTERY!!
So good luck!!
Is this a good question?