Thanks David - I did read the two mirror-related guides before posting, but for some reason I didn't see how to remove the actual covers.
I'll read them again...
Ah yes... "The black surround detaches from the painted section by the careful use of a thin blade or screwdriver. Push the black surround down and out, to unclip it."
Don't know how I missed that
I hope they're more robust than those on my 75... as I say, I have a tendency to break things