Interestingly the Macbook trackpad does not have physical buttons. It uses haptic feedback to simulate the feeling of a "click", but in reality there is no button which could be interrupted by dust.

I did have a Macbook trackpad fail in a similar way, where the "button" seemed to intermittently fail to click. It turned out my battery was swelling (see /r/spicypillows) and this impacted the trackpad operation.

On topic, I took the Macbook with swollen battery in to the Apple Store and they had to replace the entire keyboard+battery assembly as a unit because the battery was not replaceable.