a. I don't try any preventative measures.
b. Standard wheel cleaner from auto part store that says "safe for painted wheels".
c. I have drums in the back, but I believe your system should have some regulator or compensator valve (can't recall proper name) that permits more pressure to the front. That may be defective. One member put an adjustable valve in his Pagoda so play with various pressure settings to the rear brakes.
Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both tops
1994 E420