Yes, I've had this experience on other cars, both Nissan and GM. I have learned to always replace brake pads before they are worn to 50% of original thickness. As the pads wear, the caliper piston moves further in the bore to compensate. This exposes more of the microfinished piston surface to air, water, and road debris, eventually damaging it (and when it retracts, also damaging the cylinder sealing ring). The boot is just a superficial dust seal, but coating it with silicone grease helps. Since I adopted the 50% pad wear rule, I have never found it necessary to replace a caliper or resurface a rotor disc. I change my Volvo pads once a year (every 12,000 miles).