This looks like some moisture damage. To the right where the discoloration isn't as blotchy, it looks like it could just be paper oxidation. CGC is especially hard on anything that is classified as a stain, and there's not really a good option to remove it and increase the grade. But, you know what you're getting into. I've had a couple books with small stains that if I'd seen them ahead of time, and/or known how CGC would consider them, I might not have graded those books. In this case, it's not like you can go find a dozen copies of this for sale, so who cares? There's a first edition that looks like dogcrap on ebay listed for $700 raw. Find a reputable cleaner/presser, get what can be done to make it as presentable as possible, and send it to CGC. It will be a cool thing to have in a PC, or you'd probably clear the investment in clean/press/grading by a wide margin selling a slabbed copy.