Melted Cover

Wire wool should scrub it off but you might end up with a shinier bit and end up having to do the whole lot

 

Run motor up to temp and wipe it off with inside of old leather glove or similar.

 

Paint thinners got some off a silencer for me. Is that what you call it in the States??

 

Yes, any abrasive solution will affect the metal too.

Maybe something harder than the plastic but softer than the steel might work. Perhaps the white pads that you use on non-stick/teflon pans etc

 

Nah. I think paint thinners is a better bet.
Many years ago, my wife to be thought she's help clean my bike and scratched the chrome on both the Conti silencers with one of these pads

 

IME, the green pads are a total nightmare. I was once stupid enough to use one to remove ice from a windscreen and it scratched the glass. As you say, they will also scratch and remove chrome. I won't have them in the house, you may as well use sandpaper.
However, the white pads are much softer and far less destructive - are you sure it was a white pad that damaged your Contis??

 

It was probably the green ones, it was a long time ago.

 

Seems likely...

 

An image would give people a better view to offer advice.