I had the same problem with my 2003 S430 - the parking brake pedal would not stay down, so the brakes were never applied.
The "the copper colored flat wire" is one end of a stout flat spring that is coiled around a cylindrical aluminum spigot that is part of the main casting. When the pedal is pushed down, the spring should tighten where it is wrapped around the cylinder, and seize it so that the pedal is held down. At the same time, the spring presses the toothed black plastic part into contact with teeth on the cylinder, which holds the spring tightly wrapped around the cylinder. When the brake release is pulled, it pulls the black plastic part away from the teeth on the cylinder, which allows the spring to relax, which allows the pedal to return, which releases the brakes.
In the fullness of time, the end of the spring bends enough that it slips out of the slot on the black plastic piece, so that the teeth are no longer pressed together, so the spring is not held wrapped tightly around the aluminum cylinder, so the pedal is not held down, so the brakes are not applied. The diagnostic clue is that you no longer hear clicks when you press the pedal down. The repair is to either bend the spring back enough to stay in its slot in the black plastic piece (which is not easy), or to start replacing things (which is even less easy).
There should not really ever be any wear on the parking brake shoes, unless you drive with them pressed against the drum, so there should not be any need for adjustment, other than stretching of the steel cables or distortion of the cable attachments.
Georgia cars (other than those very near the coasts) rarely see salt, so few cars in our area will see rust in the parking brake system. Those who live on small islands or in colder climates do, of course, have vehicles which suffer from salt-fed steel termites...