looks like much time passed from the liquid spill. try to clean it with a soft toothbrush and isopropil alchool. and then look if board is way better or it has too much corrosion.
Oh hell that looks like some nasty liquid (chocolate milk?).
Normally I'd say avoid ultrasonic-cleaning until you've cleaned up the worst, but I think in this case you probably want to ultrasonic clean it before doing anything at all.
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