That Rotor pump should be rigid. It should fit to the center eccentric went NO GAP. As the eccentric rotates, the outside gap moves water around from the intake in the propeller hub to the water line to the powerhead.
Johnson, Mercury and others used the same system. Some ingredients used in lubrication cause the rubber to swell. this moves the gap from the water side to the eccentric side, and no water will be pumped. This from the Johnson service manual. (contributed {As I Recall} by Frank Robb)
