Try oven cleaner,...
...or,...To remove areas of light rust and oxidization on chrome and other shiny bits all you need is some aluminum foil and soapy water.
Fold up the foil into a nice little square, dip it in the soapy water, and scrub away. It leaves absolutely no scratches or swirl marks.

I got it from Fish, in the daily tip thread...

Thanks, gonna try these out... I'm assuming the muffler should be at normal air temp when cleaning or should it be slightly warm?

I tried the aluminum foil trick on my chrome and was less then impressed. Now mine just had a few light spots of rust and water spottage. Took off all the dirt, water spots and most, not all, of the tiny bits of rust. Shine seemed muted, less brilliant, duller. And dont use the trick on your aluminum engine case. Leaves lil swirls.

When I had a big splotch of road tar on mine, I took a penny too it and scraped away. Former owner said he tried "every type of chrome cleaner. couldn't get it off". 10 minutes with a penny and presto! No scratches either.

Ok the penny trick worked on the smaller stuff with no scratching and without leaving any marks. I still have a giant hunk of burnt motorcycle cover that's pretty thick and the penny won't even dent it!

Glad to hear! Splotches on the muffler can really rack the nerves!

I actually had some motorcycle cover melter to my exhaust at one point as well, foolish me put the cover on too early at one point. Similar experience, penny certainly didn't do the job on it. I used a glass scraper, but that did result in a few minor scratches. Never though about heating it up first to wipe it off, good insight for future reference.