Well, maybe I should have mentioned it earlier, but whatever. The black color is only visible through the polarizing film. When I took it apart, I could see the intended shapes on the LCD as well as this liquid, no obvious crack, so I doubt it's oxidation, but still probably not fixable.
It may not be cracked, it might just be the two pieces of glass separating slightly along the side exposing the liquid crystal (likely not visible to the naked eye). But either way, it's unfixable without the equipment used to actually manufacture LCD screens. The liquid crystal is never visible without the polarizing filters. I suspect it was damaged in some way by being dropped, and the black 'cloud' will likely get larger over time.
In theory, you could actually separate the glass layers, clean out the crystal completely and still be able to see the sprites (barely), but they'd be damn hard to photograph like that. They are sort of etched into the glass (I assumed it's a conductive material bonded to the glass, never really looked into who these are manufactured...) Not the easiest solution, but usable if there's no other option.
The circuit board looks fine though, the weird stippling you see on it is just how the green 'paint' layer was applied (or dried) when it was manufactured.
Did you remove the speaker to see if there's markings on the chip on that side?