I don't even know where to start.

If you know how to work with Channels, look at the Red Channel -- it has fewer spots/smudges to clean up and no colored stains. Then just work on the damaged areas, and bring the young man's face out of the shadows somewhat.

I guess I can forget about any kind of detail.

I did some masked curves and some healing brush, although a higher-res image hould heal better.

there may be more efficient ways to approach this...

but as far as using the stamp tool on this I would set the mode to lighten and just select the sample point a couple of pixels over... the soft brush set at about 45% opacity..

this way you won't be removing all the pixels just the dark ones..
good luck
RonDon