The mouse clicks on my old 2010 17in MBP have been getting less and less clicky of late. The machine doesn’t get much use, it’s my “sitting in front of the TV doing some work” machine.
I assumed it was dust getting under the trackpad thing, so bought some compressed air canisters and gave it a blast, no change. So I figured I’d pull the back off, lift the battery and give the mousepad a blast from the inside. Only to discover the battery has swollen, quite a lot, and it was pushing the trackpad up and stopping it clicking. Did some Googling and it seems a common issue, and the trackpad getting less clicky is a classic indication that the battery is swelling, which if left to swells too much can pretty much trash the Mac.
So, word of warning… If your trackpad/mousepad thing is less clicky than it used to be, check the battery.
A new one cost me £50, if I hadn’t checked, the repair bill might have been much much higher!