Impeller replacement.
Scott, Others will tell you specifically what to look for when replacing the impeller on your A-4 so I will share with you a cautionary tale. On two occasions in my sailing life and on two separate boats, coincidentally both E31's, the water pump failed to work when I knew the pump body and impeller were in good repair and the raw water intake path was clear. In both cases the culprit was an air lock. The simple solution was for me to remove the uppermost hose attached to the pump, elevate it to its fullest vertical extent and using a plastic tumbler, I filled it with water from the galley sink. I placed my thumb over the end of the now full hose and in one movement, attached it with haste to the pump barb. In both cases that's all it took and the pump instantly came back to life (check the exhaust flange for acceptable water flow as proof). With your boat having been on the hard, there's every chance that your hoses and pump could have developed an air lock. You now know the work-around for that. As a matter of fact once you get your boat in the water, why not just fill the hose from the start so you can check that worry off your list? Good luck, Glyn Judson, E31 hull #55, Marina del Rey CA