I have a 1hp 2-wire 240V submersible 4" pump installed in a PVC-cased 6" well. It was installed 6yrs ago. The original pump/motor was a red jacket grizzly with Franklin motor. After 3yrs it failed (locked rotor) and when I pulled it out the case was visibly corroded with holes in it. The pump itself looked fine

3 year old well pump motor case corroded so badly it seized up?

I replaced the Franklin with a same-sized Grundfos which operated fine until I turned it on last weekend for the first time since winter. No water. I pulled it out and it also had a locked rotor and the same case corrosion.

3yr old SS pump motor corroded AGAIN

The well is connected to a lawn irrigation system and has plenty of sulfur that you can smell and see the residue. I measured the pH at the top of the water table and it was 7.3.

After seeing pics of the corrosion the pump guys thought this should be posted in an Electrical forum as well.

I really really really need to keep this from happening again.

Pics of the 3-yr-old failed Grundfos: