Mansfield EcoQuantum flushing problem?

We've had nothing but problems with one of the toilets we've installed. Sometimes it flushes, sometimes it doesn't, and the problem seems to be with the handle. When it's not flushing I have to take the tank lid off and jiggle the small mechanism right on the other side of the handle. It will eventually flush if I jiggle it long enough and simultaneously pull up (or down) on the handle, but I want to fix the problem, not treat the symptom. Can't find any online help.