After reading this thread, I pulled one pair of front pads and, no surprise, two frozen pistons. Ordered parts - disassembled, and found it very difficult to clean the stains from the inside of the caliper. Is that a "hard chrome" finish in there? The pistons where equally nasty but cleaned well with brake clean, a polish with "Nox
on" and then a very lite buffing with White Rouge, followed by another wash with brake clean to remove any polish compound. Although the pistons now seem to work and feel fine in the calipers, I would like to remove all the stain, any ideas?