I'd be inclined to use a liquid penetrating oil rather than a spray one like WD-40, as it's so close to the fretboard. The humble 3 in 1 is a penetrating oil that may do the job, and if that fails, you could move up to PlusGas liquid. Ideally, take the neck off. Mask off the fretboard and, if you can, form a dam around the spoke wheel.