Photoshop :: Repairing Old Grey Scanned Photo

I am using Photoshop CS8 (and also have Photoshop Elements) with Windows 7.
 
I am trying to repair an old image which is about 40-yrs-old (please see below). The original image that was scanned in was a lot more uniform grey, but I have managed to add a little more contrast.
 
However, much still needs to be done. I was going to attempt to remove the stain on the right using the clone tool, but my main concern is to replace the sky. This would add some clouds, a little contrast, and remove the scratch at the top of the photo.
 
However, when I try to remove this old, dull sky using Photoshop Elements's magic wand based on this tutorial
 
[URL].....
 
I find that the wand also removes the head and body of the duck due, no doubt, to the similarity of grey tones.
 
How to replace this dull sky with a more interesting one, but I am not sure how to do so while keeping my duck. In fact, I would like to emphasise the presence of the duck more. Should I use a mask technique (I am not very good at masks, I am afraid) to mask the duck from the changes that a new sky will bring about?