I take it then you're XR8 didn't come with scheduled servicing (AU3?)
To be honest, chain places like Ultra Tune, Midas etc can just be us dodgy, if not dodgier than a Ford Dealer - they have to deal with more car manufacturers and models than just Fords.
Try a local dealer, and if you're not happy with them try another one. Where in Sydney are you? Others might recommend dealers they've had good experiences with close by. As far as services go, Sinclair Ford have been pretty good to me - couple of minor issues with warranty stuff, but nothing that hasn't been cleared up easily.
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