While investigating a sticking hand brake mechanism on my TF (sorted) I discovered that both rear discs were rusty on the inboard side over the outer half of the pad's swept area. On further investigation I found that the pads on the inside had been installed incorrectly, in that the cylinders had not been aligned correctly, ie with the four cutouts aligned at 12, 3, 6 and 9 o'clock. this caused the cylinders to contact the lug on the back of the pad and therefor in effect only forcing the bottom of the pad onto the disc when braking. This shows how IMPORTANT it is to align up the piston correctly. I cannot blame the PO as it was done by the dealer who sold me the car.