WD40 won't help here, get a thick washer, or thin bit of flat metal.
Now after removing the clamp bolt holding the strut to the hub, put the bolt back in from the opposite side, it the THREADED side instead of the hole, now with the bit of metal/washer insert in the slit of the hub, so that as the bolt is wound in it hits the metal/washer, now when turning this bolt it opens up the slit and the hub will literally fall off.
Don't open as far as you can, just enough so it knocks off ok.
Yes you can use a chisel to widen the slit, but this is safer, and doesn't run the risk of hurting yourself if you miss with the hammer
tabetha