S100 engine brightener. It claims it brings back the factory black look. - YouTube
Dr. Wack S100 Bio Motor Cleaner 750 ml Removes Stubborn Dirt Such as Oil, Insects or Fat Residues, 97% Natural Raw Materials, High-quality Engine Care, Made in Germany : Amazon.nl: Automotive
S100 Engine Brightener - 19200A Dirt Bike Motorcycle Goldwing - Dennis Kirk