Complex sentence: Hubbard taught that thetans left human bodies after they died and went to an "implant stations", among which was a location on a planet near Earth, where their memories were erased.
Split into simpler sentences: Hubbard taught that thetans left human bodies after they died. The thetans were then said to go to an "implant station", among which was a location on a planet near Earth, where their memories were erased.