Let me also throw another wrench into this one, when I replaced the pump the 1" barb fitting to the pitless adapter was galvanized and so rusty it was probably half or less of its original size inside. I think its safe to say it wasn't the original pump by the looks of it but I'm assuming the pitless wasn't replaced when the old pump was so I'm thinking that fitting probably looks the same or worse. Would this factor into anything?
Also thinking about it could it be the fact it's only the 2 hot wires no ground running from the house to the case. The ground they have running to the pump is just draped over the edge of the case. In my line of work grounds are most important, seems strange to me not to have 2 hots and a ground.