I bought a 341 style rear fender from the USA and the chrome was in really good condition but had the usual surface rust underneath which I wanted to remove. I was recommended to use a product called 'Deox-C' by a friend who runs a local engineering company. I dipped the fender in it for about 48 hours, as I was assured that the chrome would not be damaged in any way. I have to say that the stuff is magic because it removed all of the rust but no base metal or Chrome. I think they also sell it in Gel form too.
http://www.bilthamber.com/deoxc.html
