I recently did this restoration and it was a breeze because the blue channel was hardly affected by the "stain"on the left side of the photo.
(http://i1067.photobucket.com/albums/u426/jaytrumpet/Blue%20Channel/McColeJ_21_20_3_5x5_zpsc4778b57.jpg) (http://s1067.photobucket.com/user/jaytrumpet/media/Blue%20Channel/McColeJ_21_20_3_5x5_zpsc4778b57.jpg.html)
I went to the channels panel and isolated and copied the blue channel, went back to the layers panel, created a new layer and pasted it in. I then set the layer's blend mode to "darken" an it worked nicely.
(http://i1067.photobucket.com/albums/u426/jaytrumpet/Blue%20Channel/McColeJ_21_20_3_5x5_JL_zps5c523f31.jpg) (http://s1067.photobucket.com/user/jaytrumpet/media/Blue%20Channel/McColeJ_21_20_3_5x5_JL_zps5c523f31.jpg.html)
Still had to get rid of a lot of gunk with the patch and clone tools, but at least I avoided having to fully recreate the curtains on the left side.