is that stuff on the back corrosion (eating the metal away) or is it just material caked onto it? No luck cleaning it any better huh?
Possibly try the peroxide cleaning method to loosen that stuff up. If you don;t know what that is, just get a bottle of hydrogen peroxide and pour enough to cover the item in a microwavable container and put it in the microwave for 2 to 3 minutes until the peroxide is nice and hot (bubbling or almost) DO NOT MICROWAVE WITH THE OBJECT IN THE SOLUTION!!! Just the peroxide in the microwave in a safe container. Carefully take the solution out of the nuker and carefully place the item in the peroxide. It will start fizzing around the object and that is it working. LEave for about an hour or so and take it out and clean with Q-tips. Make sure the Q-tips are dipped into the peroxide first so they are wet. Helps the cleaning.
Hope this helps you.
FUnkman