If you need to go to a larger bore size due to bore damage or pitting, there is a way to repair old bores. ¹⁾
Especially on hard to find, expensive or antique masters, this is an alternative.

You can buy bushings that are either spot on or require very little machine work.
Basically, you turn it a couple of thousandths bigger than the bore.
The bore, if pitted badly can be dressed with a brake hone but a baby smooth finish is not required.
The master is baked to around 350-400°F and the bushing is frozen to aid in assembly.
You can use high temp thread lock as a lube to install the bushing and when it sets up, it prevents back leaks.
To stabilize the bushing, run a dowel rod tightly in the bore and use a live center to align with the jaws.
The wood can be drilled out but a little oil soak or grease will aid removal.
Then, standard repair kits will work inside the new bushing.

^{2) 3) 4)}

A Parker brass flared fitting gasket is basically a flared brass washer. Suitable for use in air, water, and oil applications.

The 1974-1977 pie caliper below has a damaged flare seat that was repaired using a 3/16“ flare gasket.
So if the flared seat is damaged and leaking and before trashing the caliper, there's a chance it can be sealed using one of these.
⁵⁾