A couple notes after reading thru this:
As Graham mentioned it is the seal groove that is important, not the cylinder bore. The bore must be clean to allow the piston to slide freely but it is the seal groove that the seal works against... and the piston sides of course. The groove must be clean, no pits or deep scratches. The piston sides must be smooth with no pits or deep scratches parallel to the axis.
PMB Performance rebuilds Porsche calipers primarily but also do other makes. They have a good tech page which describes the rebuild process:
https://pmbperformance.com/pages/the-ultimate-brake-caliper-restoration-guide
They are not as familiar with Mercedes calipers as they are Porsche so it would be wise to inspect the calipers post rebuild, if you have them do it, for correct piston orientation and dust seal installation... direct experience here. Their plating process is nice. Direct experience also requires me to say that the plating is important in reducing corrosion that will lock up your calipers again in a relatively short time since they do see water exposure externally and brake fluid is hygroscopic, it absorbs moisture. Many lower end caliper rebuilders that supply the corner auto parts stores do not re-plate and you'll find you have sticky calipers within a short time. Make sure the reservoir cap bellows is in good shape and that you replace the fluid every two years or so to remove the inevitable accumulated moisture.