d23,
Two good possibilities for what you're looking for is : REDDA and Centrilift. Both located in Tulsa Oklahoma, I believe. These companies specialize in 3500 RPM deep well pumps. Although most of their work is in the oilfield business, both have done some work in water wells. I can't give you...
PumpDesigner,
My guess would be a combination of corrosion and erosion. It would be interesting to see what the impellers look like, since they probably are bronze. Also, the wear ring area (suction side) of the impeller and bowl should give some clues, especially if the pump has a stainless...
