Hmm... I'll bet it's rotor's needing machining. HSV's tend to eat rotor's... side affect of stopping big, heavy 1600kg+ cars in relatively short distances.
Two HSV's I've had with the "Performance" brake package (VT2 Clubby R8 and my current VZ2 XUV) I'd get between 15,000 and 20,000k between machining... the one that I've had with the "Premium" or big brake kit (GTO s2) got a bit over that, but the rotors were basically stuffed and up for replacement at just past 80,000k.
Simple to check - run thumb nail across the rotor, and if it drags on ridges then they most probably need machining.
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