Are the bearings sealed? If so then the only real solution (other than replacing them) is a very small bearing packer (I have one from my model helicopter days) to force grease through the seals.
Also WD40 is crap...try some Fluid Film, it won't evaporate like WD will since it has no solvents.
Yes I cringe every time I hear someone using WD as a lubricant. Use a real lubricant. A real good anti-seize to loosen it up then something more substantial after that.