To OP, if the rotors are grooved, its possible that the pads that were fitted might have been too aggressive for the stock rotors? Since I assume the grooving happened over time rather than recent so the pads can't be too aggressive though? 18mths is. Unfortunately to improve braking performance, usually pads get more aggressive and therefore wear the rotors down more.
There are quite a few pads that cater for your requirement [Everything OEM is but better]
e.g Endless - NS97, SSM [I'm not familiar with Aussie brands]