Yesterday I gave the Z a good washing
I also tried out the Adam's Invisible Undercarriage product. Unfortunately, I only had time for one wheel well
It took two applications of their All Purpose cleaner to prep the linings for treatment (almost 50K miles worth of dirt). It looks fantastic so far, but I am really hoping that it lasts a while. It makes it looks new again, very similar to my experience with their VRT on the plastic bits under the hood