I still like my mental image that there is a semi-floating mass behind the ball, Blue. Perhaps if you depress the ball slightly with a probe and hose in some carb cleaner from the front into the cavity behind the ball, you'll break up whatever it is? Don't push that ball far, though: the cavity is tapered, probably to facilitate moulding the plastic part concerned, so once you push it back far enough to stick, I don't know how to get it out.
