...560 SEC? And will the years be significant? The mirror is from a '90 420 SEL.
The mirror isn't for ME, I have an extra one that I was going to give to someone.

I have an SEC. I also have an idea that the mirrors on the sedans are different but I could be wrong. The best thing to do is to try it. It's the thought that counts.

Good used parts available in the USA from buyMBparts.com located in Georgia if I recall correctly.

In Australia from MB Spares Service located in Canberra.

There are probably other specialist MB dismantlers elsewhere. Those are the two I know of.

I don't see why not.
The SEC is just a Coupe version of the SEL, so they should be similar.