Ok. According to these guys it isn't needed....Have never seen one of those screws break unless it was by someone trying to remove it by turning the wrong direction. Many years ago (decades really) I broke one on the first pump I encountered that had one. It was on a older StaRite, but they used brass screws then. I unscrewed the impeller, not knowing it was there and broke it off. All new ones are stainless and I have no idea how it could break under normal use. Have seen many eaten away by bad water chemistry, particularly when a tab feeder was in the system.
Something else is going on, but you can't run the pump without it or the motor will be damaged.