Looks like you can buy individual parts to rebuild that pump. Including the shaft.
http://www.downwindmarine.com/Oberd...eller-Pump-Onan-4.0-Generator-p-91002306.html
http://www.downwindmarine.com/Oberdorfer-Service-Parts-Rubber-Impeller-Pumps-p-91002431.html
http://www.downwindmarine.com/Oberd...eller-Pump-Onan-4.0-Generator-p-91002306.html
http://www.downwindmarine.com/Oberdorfer-Service-Parts-Rubber-Impeller-Pumps-p-91002431.html