Audi S3 - refund wanted?

I took delivery of an Audi S3 sedan MY14 in November 2014 and have had mechanical problems since day 1. The car has spent 15 weeks in the Audi workshop in the 8 months I've had it and there is no end in sight. Audi admits they can't find the problem, despite hearing it when I took a mechanic for a test-drive.

They've so far replaced part of the wiring harness, something in the engine that was leaking coolant, and the throttle potentiometer. The car has a three-year warranty and the dealership has given me an extra two years for my troubles. The car is due in once again next week.

Each time they can’t predict how long it will be in the shop. I've been told six weeks minimum this round. I am given a loan car each time, which helps ease the inconvenience, but this isn't fixing the problems with my car.

I have called Audi Australia to discuss product quality, but they keep saying it's a dealership issue and that they'll work with me to resolve it, but they're dragging their knuckles. The dealership says it's a manufacturer's issue and they'll keep fixing it until they get it right. I have contacted Consumer Affairs and apparently I have no rights in this as there are no lemon laws in Australia.

The Consumer Law Act 2011 says if a product is faulty or fails to do its job then the consumer is entitled to a refund, but CA also said any refund would be at the dealership's discretion, unless I can get an independent diagnosis done and present it to them. But getting another party involved at this stage makes me nervous that Audi will use it as an excuse to back away from their responsibilities. And besides, as a customer I have a right to have it fixed without having to shop elsewhere for a diagnosis and tell Audi how to do their job. They pay their boys enough for that.
Any ideas as to how I can handle this? Taking them to court would be a lengthy process and costly too, but minding my manners and staying patient isn't getting me anywhere either.