As a temporary measure, you can place a couple of washers on the retaining rod between that impeller and the top of the unit, raising it a couple of millimeters and allowing the non-worn part of the teeth to engage with the gears.
If you pulled whole unit out where you exposed the glass balls you probably did not replace it correctly. The balls have to be situated correctly trick to putting then back in place. Maybe someone here can explain the procedure..you have to take out and replace one by one as you rotate the impeller.
