Carryfast:
Swarfega, or preferably Tufanega the orange one with the granules, hand cleaner.Put plenty of it on a rag wrap it and run it all around the wheel a few times and then clean it off with another one soaked with just water.
Why is it that some vehicles have every switch and control item is covered in that grey/brown gunge - when I did plating work it was very common and very gross.
Just wrap the wheel in cling wrap as an emergency fix.
Use the cleanser on a small stiff bristled brush - it brings greasy hi-viz gear up a treat.