I am rebuilding my Brakes on an 83 240D from a pair of ATE's I found in a junkyard. One of the calipers was stuck so bad, I had to use a huge pair of vise grips to extract it.
Unfortunately, I chewed up and marred the top 3/16" of the machined piston area (no to be confused with the non-machined ridged area that sits on the top of the piston).
I still think I can still use this piston because the top 3/16" of the brake piston's machined area sits above the line where the caliper's internal seal seals the piston.
Does anyone know if I can?

Finally does anyone know what comes in an ATE rebuild kit?
I was curious and took one pair of the two calipers and unbolted the two halves apart to see what the cross section looked like. There are two internal orifices that will now need O rings when I rebolt the two halves. Does the ATE kit have these parts?