If you have any, acetone (nail polish remover) is a more aggressive solvent which could be worth a try. And brushing it in with a toothbrush can help. I bought a number of cheap toothbrushes just dedicated to guitar brushing purposes.

I don't think your neck has any binding on, but be aware that acetone does soften and (eventually) dissolve binding, so maybe avoid using it if that's the case.