Hi Murray,
You should have protections under Australian Consumer Law. The car should be free from defects and last a reasonable amount of time. The determination of reasonable would depend on the age and mileage of the car.
You could try writing a letter of demand to have the defective parts replaced with new parts and state that second hand parts prone to failure will not be acceptable. NSW Fair trading will expect you to have formally initiated communication and if you don't get a positive response from the dealer then lodge a complaint with Fair trading.
Some more detail can be found here:
Motor_vehicle_warranty_and_repair_disputes
I don't like your chances of a refund without following this process.
