Generally
Factory refurbished Bendix brake servo complete with 4 bolt master cylinder.
The master cylinder is lined with a brass lining that can always be damaged by rust. It happens that the renovation company mills a larger hole in the cylinder, then a brass tube is pressed into the main cylinder, which is then drilled to the original dimension. After that, everything is assembled with new seals and the piston is also replaced if there is damage to the old one. This method results in a wear-resistant master cylinder with original diameter and function like a factory new master cylinder.
Note! The master cylinder that sits on the brake servo is delivered without a screw cap, so the picture is not correct.