I don't recommend the WD-40 trick as it will only make a mess. The oil in it will act like a magnet collecting the dust and debris around your system.
While its some work you can take the track pad out and clean it properly and make sure it's OK (and if needed carefully lube the pivot-point).
The root issue is something either is jamming it or something was spilled onto the click button.
Lastly, the battery could have swelled-up pushing on the trackpad from below.