Wow!
How filthy can one derailleur get? This one looks like it had a bath in black moly lube and dirt. Degraded aluminum bits and grease that really needed some cleaning. I have the parts out of the solvent and a few items are going to get some protective paint before going back together. The adjustor screws will be replaced with stainless steel since they get a lot of dirt and water contamination.
The cleaning solvent after a first wash. Notice how black the solvent is from the dirt and degraded aluminum that was on the derailleur. A second wash and some cleaning and parts will get a clear coat to protect the finish.
After the parts are clear coated and new screws sourced I will post some pictures of the re-assembly. Smiles, MH