Being a machinist, you would understand how to spot face the sealing surface on the calipers right? if they are scratched or pitted then you can correct that rather quickly. If you like you could give them the concentric rings to seal (they called it a phonographic finish in the big machine shop I worked at), or just clean and flat, and perpendicular to the bolt hole will seal too.
To clean the scale off the washers a scotch Britte works too, or put them in your pocket with your change for a day. If you heat them dull read and quench in water, often all the scale will fall off right then.
Grigg
