The shaft can only be replaced by a new motor, it is not sold as a separate part as they press it into the motor when the motor is built. Please send it in, be sure to include the drive unit with shaft and the motor and I will do my best to remove it and reinstall the shaft in the motor. To prevent this in the future, be sure to remove the drive unit and soak the motor and drive unit in vinegar and water 50/50 at least every 6 months and as often as every 3 depending on KH and Calcium. Be sure to include a note with your return address and phone number.
Tunze USA
305 Victor St
Austin, TX 78753