You're all about right,, no rust any where.. ali corrosion .. it was behind the seal..and near the dust cover, the Ali had white powder, formed behind the seal causing it to pinch the piston,... the piston also had some white goo on it
Caliper on the bench.. I could see that the seal was bulging out and it was impossible to even put the piston back inside.. Removed the seal.. cleaned the groove out and it all went back together... with a bit of cursing.. as everything covered in oil makes it a nightmare to hold on to.. Oily rubber and plated steel, and screwing the piston back in was interesting to say the least.. Put it back on the car ,bleed the brakes, Fitted new pads and it's happy again... So I'm I .. as it took a couple of hours And the pads were just £4.20..! And they ..have done both sides..
