Stop!!...
Listen up people, you don't have replace the whole upper case.....
Come on rab777hp and others, that's your answer for everything, the screen doesn't work replace the whole upper case. The keyboard is sticky replace the whole upper case. The super-driver doesn't work replace the whole upper case. Just cut it out if you don't know, don't misguide others. Everyone comes for some guardians how to trouble shoot and fix there problems.
Time to trouble shoot.
Q. Has the MB had a liquid spill?
A. It could be few things:1. the trackpad might still have liquid which would need to be clean with some alcohol and air dried. 2. the connectors might be dirty they'll need to be clean. 3. the worst thing could be that connector ribbon is fryed, but no problem you could buy that ribbon on eBay or even here ifixit.
Q. Is the trackpad center? Or leaning closer to one edge?
A. Might be the trackpad need to be readjusted. Just follow the step by step guide to do that.
Q. Have you dissemble the trackpad or the MB before?
A. It might be the ribbon wasn't properly placed, things do happen.
Q. Has the trackpad malfunction before since you has the MB?
A. It just might be the trackpad itself they do fail, but you could always replace it.
If you follow the step by step guide, you'll be fine doing it yourself. Hey it's better then buying the whole uppercase. Do the math $250 to $80 I know you'll pick $80. If you where to choose to replace the upper case alot more work you'll have to do.
Just to let you know are going to need a special screwdriver for the trackpad. You could find the screwdriver at electronic store.
Hope that helps. Good luck with that.