sworkscooper

Well I can only refer to the only four pot caliper I have experience on , that being the London Taxi ( Black cab ) . They had a tendency to corrosion on the pistons and if you were careful and the corrosion not too crusty , you could clean the pistons and free them off . The outer 'Wiper' seal had a flimsy metal retainer that needed to be pressed into place when overhauling the calipers and yes they were an absolute pain to fit as they would kink and bend out of shape if care wasn't taken . The Wiper seal and the inner seal over time become dry and obviously contaminated with crud so it will help if you spray a bit of WD on the piston and work them in and out as best you can . It goes without saying that being a safety critical item , they need to be equal in their movement as brake imbalance / pulling will come into play as I'm sure you are aware.