Need help troubleshooting problem with brakes

One of the problems with bleeding brakes in old cars is this. Detroit used their wonder metal, cast iron, for a lot of m/cyls. They rust from moisture absorbed, build up a rust pile in the mcl. When you bleed the brakes, bottoming the pistons in the mcl, seals get ripped when they pass over the rust. Then strange problems occur. Not saying this is the problem, but when everything else checks out, it is likely time for a new mcl.