He replaced it because he couldn't afford for it to "act up" again. One of these motors he had the springs that hold the carbon brushes snap from rust. Like yours, his was full of corrosion inside. In fact, all three he has had, had extensive corrosion inside. As you said, the aluminum is a poor ground. There is an aluminum base plate on the motor, which mates to the cast aluminum base (the pump mount). The copper wires connected to the carbon brushes on all 3 of his motors were green with corrosion. When he spoke to the dealer, he mentioned I was going to weld on a nut to the motor housing, to attach another ground to it. The dealer said it wouldn't work, unless it was attached properly to the inside of the motor. Perhaps Finnegan can tell you where to attach a ground lead to, internally on the motor. I like to work on things, but the time frame here was too short for me to make sure he would have no trouble, and the snow was waiting to be plowed. He plowed from 10 PM, until the dealer opened at 8 AM. I can go over the old motor, and weld on the nut, and keep it as a spare. I think because the E-60 mounts sideways, it allows moisture in easier. There is no seal or gasket on the "end cap" of the motor. The old E-47 mounts vertically, so moisture is not as much of a problem.
~Chuck