Watchmakers International regarding this. I am not an expert but just thinking about this, perhaps there is not a "case tube" for the Super Oyster, but a gasket and seal system instead. I seem to recall that when installing screw down crowns in the Super Oysters it required drilling out the case to make room for the case tube. If I am correct, your watch can not be converted back to the old system. I appreciate your purist intent...at the same time, Rolex certainly had no qualms about abandoning the Super Oyster system. Perhaps a better idea is just to find another watch that is still in its Super Oyster configuration and then have one of each.