Quoted from ALY:Saying bad coil stopper is responsible for weak flippers is like saying your car has less horse-power because of bad brakes.
It is on sterns. The stopper actually breaks off the bracket and gets magnetized to the plunger. It’ll look fine at first glance, then when you move the flipper by hand you can watch the stopper move into the coil. Had it happen on DP and AIQ so far. First sign is the little brass shavings in the cabinet directly below the flippers.