my project bike, 84 Nighthawk, has a 40 year old, faded, grayish, light 'used to be black' motor. It has lost its shine over the years. I had never used one of the 'engine brightener' products but figured it's worth a try. I cleaned and degreased my motor..then used some S100 engine cleaner...dried it off with a small blower/vac...and sprayed the black parts with the S100 Engine Brightener.
It kind of looks like a shiny clear coat that makes dull black look glossy. I'm sure it will fade over time and it's probably over priced, but dang, it sure looks good! My bike doesn't get wet so I'll see how long it lasts..
before and after pics..