My trackpad had become extremely hard to click and took a lot of force to do any clicking. So, I decided to replace the pad and upgrade the RAM while I was inside the computer.
The repair was simple and easy and took about 25 minutes to complete. I even did a lot of cleaning inside the computer while I had it open to remove dust and grime.
The big ah-ha moment for me came when I installed the new trackpad and felt that great clicking sound again. It worked great until I reassembled the entire computer and found that the new trackpad wouldn't click either. After a few minutes of troubleshooting, I found that my battery had swollen and was pressing against the trackpad preventing it from clicking. I ordered a new battery and all is well. Bottom line, check your battery for swelling before you replace your trackpad.
PC3-8500 2 GB RAM Chip
Tri-point Y0 Screwdriver
Tri-point Y1 Screwdriver
MacBook Unibody (A1278) Trackpad