I have a shallow well pump, convertible jet, on a sandpoint at the cottage. After sitting for the week unused it sometimes seizes, just sits buzzing, at which point I quickly turn the power off. I can turn the motor manually using a screwdriver to rotate the fan through the ventilation holes in the housing, obviously with the breaker OFF. It feels a bit stiff at first but after a couple of rotations frees up somewhat. When I turn the breaker back on the pump will start and then continue to run flawlessly while we are there. Any ideas what may be causing this? Should I dismantle and clean the pump or is it probably time for a new one?