As for how many after market shaker motors got out before the needed capacitor removal fix was addressed I can not say. I can say that only 12 units from Pinball Life left the building.
Of the 12 only 2 had been installed before we learned of the issue. We replaced the node board on these 2 customers' machines ASAP. The other 10 customers simply snipped the capacitor off before installing the kit. There have been no issues since.
There is no voltage difference/issue between the SAM and SPIKE system shaker motors. Shake motors are a pretty simple animal; metal weights placed off center from gravity spin from an axel causing the game to shake. As long as the motor's voltage rating and RPMS are correct you are good to go. SAM system shaker kits require a grounding cap, SPIKE kits do not.
I would like to add that Stern heard of this early grounding issue first and they called me to let me know it was happening. I think that was very nice and responsible of them.