Bob, Tosh and others,
I managed, at the time of restoration, to replace these trim pieces at a reasonable price. I believe they are made of clear-anodized aluminum.
The good news is that being aluminum, they are easy (well, in a relative sense to a skilled craftsman!) to work. In the process however, particularly in re-polishing, the anodizing will be compromised. That only means you might need to, on occasion, take some metal polish to it to keep it looking tip-top.
It's astounding at how much abuse this one piece of trim receives even in a carefully owned car!
Michael Salemi
1969 280SL
Signal Red 568G w/Black Leather (Restored)
President, International Stars Section
Mercedes-Benz Club of America