Once the main rotor is removed, the drive gear and shaft can be removed by first removing the small brass collar at the bottom of the shaft. After the shaft has been pulled out remove the two flanged brass bearing at both ends of the rotor shaft mount (shown below being removed with the dental pick). Then push the large drive gear off of the steel shaft. Save the flat washers (2); one is at the top between the drive gear and the brass bearing and the other is at the bottom, between the brass collar and the brass bearing. We'll be re-installing the flat washers into the same positions during re-assembly, but the bushings can be discarded as they will be replaced with the ball bearings.