Remove selective cast/stain

[grits]

I did not use G'MIC. In gimp, colors > components > decompose. Choose the red layer. Change Image > mode to RGB.

Then I painted on a new layer, as above, and set it to mode- Color, Opacity- 65%. 

Decompose made a perfect monochrome layer to work with.

I used the original image, above, the image on the right, but you could probably get better highlights with the one on the left.

I could of done a better job of painting, I know.