Go to the Honda shop and buy a can of the spray Honda Chrome Polish. Stuff is miracle polish, I swear. Learned about it from car show people. Cost $5.95 for a huge can.
Oven cleaner works good on the bad stuff. Had a plastic grocery bag catch and melt on pipes. Oven cleaner took it right off and did not damage the chrome.
I think the black spots on the exhaust on my bike is from the drivebelt. I see much more of this on my left side exhaust than the right side. I've had some luck with WD-40 and light use of 0000 steel wool. I saw lots of these spots when my FLHRCI was brand new and less as time goes by and the mileage adds up. I just cleaned some off this am from yesterday's ride.
Always start with the least aggressive method....Most chrome can be cleaned with soap water and a Magic Eraser..if not try Polishing Soap.....if something you want to use has "steel" in the name, that should be your last resort.
I totally agree! Why risk compromising the chrome plating if it isn;t neccessary. That layer of chrome is only so thick and won't hold up to continued abrasives and will eventually wear through. Also, micromarring, argh.