Walt,
my car had the mouse nest, too! When I first got it, my wife complained of being sprayed with grit from the air vent, so I opened it up and there was the nest in the passenger side air duct. I think it was a fairly old nest. The car was brought into the US in about 1980/81, but the nest included pieces from a German horse race betting guide.
George Davis
'69 280 SL Euro manual