Actually, I think you aren't going to win this one. The problem with backs is that due to lack of use, the rear brake pad 9usually the inside one) corrodes along it's edges, and sticks to the caliper, seizing it bad enough that the piston will struggle to push it close to the disc, and then causing the disc to corrode on it's inner surface. And Ian Grieve's get out clause is that you have had very lttle use of the car, and most probably was the car regularly washed, so promoting the corrosion to seize the pad.