Sticking 5K rear brakes

[Kneale Brownson <knotnook@traverse.com>]

I replaced the master cylinder on my 5kcstq after advise from the list to
others indicated a brake that would not release after use most likely would
result from deterioration from the seals in the MC.  Mine looked like it
might be original and my 12-year-old car has nearly 190K miles.  

Anyway, brake performance is marginally better (It wasn't bad before except
for the overheating rear passenger wheel), but that brake still seems to
hang up, although  not quite as much as before.  Perhaps all the bleeding
got the moisture out and that helps some.  The caliper and rotor were
replaced on both rear wheels last fall, when the emergency brake cables
were disconnected because that system had succumbed to Michigan's road
salting.    

In reviewing the brake system via Bentley and the family CD album, I see
pressure regulators at the back on both the driver side (the adjustable one
whose setting is outlined in Bentley) and the passenger side, where my
problem is. The one behind the driver, through which all the braking action
apparently passes before the lines split and head toward each wheel, is a
block of rust.  The spring is intact, but I can't budge the part it's
attached to.   The passenger one has no external adjustment feature.  Do
these play a part in the release of  braking action, or do I have a problem
elsewhere?

Thanks, Kneale Brownson