Two guesses
If the pulsator shaft was not removed by hand:
1) Then the oil seal failed and water did get into the shaft , the shaft froze in the bearing , thereby not letting any water down into the mechanism but when the pulsator nut was removed the shaft being weakend through rusting snapped inside the bearing of the spin tube.
2) The lady was addicted to Oxydol and the pulsator, nut, shaft and boots were dissolved away by the Oxydol! Simple Boom Boom Done.