1994 Nissan Maxima spindle nut removal

I want to remove the rear right hub on the above car to replace a lug nut. I removed the dust cap and the cotter pins but the spindle nut will not come off. I used an 1/2 inch drive and socket and have tried both directions. I can move it about 1/8 inch one way. Any suggestions or tricks that I don't know about. I sprayed a penetrating oil on the threads. Thanks.