Stray blobs or smears of glue can get into unexpected places, places that are long way from anything where glue was intentionally applied. It might be worth just double checking that it really isn't glue. Slainte.Clearly not glue, it's around the head of the guitar, nothing to glue.
Grey marks, small or extensive, may be a fungal stain. Sycamore, which is in in the same Acer genus is also therefore a maple, and maples in general are susceptible to rapid fungal (mould) attack if the wood surface gets wet and isn't subsequently dried off pretty rapidly.Interestingly i had a bit of maple to plane up the other day. My first time with maple. I ran it through the thicknesser ( after flattening with planer ) and there were little grey splodges that remained until I'd taken off maybe 3 or 4mm. Is that normal with maple?