On your pumps calcium and sand had cemented the drive units to the shaft, the build up was in the hole in the drive unit where it spins on the shaft. Please double check that area. Basically once sand gets in, the run hotter and calcium sticks to the sand and eventually it forms a cement. You will need to clean the hole with vinegar and a small brush (pipe cleaner), you made need to use a small drill bit to ream it out.