Craig, I just finished doing this on a 66 C20 I picked up a few weeks ago. The socket is just a big big socket with 8 teeth (I think it is 8) that fit into the slots on the nut. Cost about $10 at O'Reilly's, my NAPA store didn't have it. The oil leaking out is completely normal, it is open from the differential to the axle ends and it is designed that way to lube the bearings at the wheel hub. I had a tough time getting mine off, too. Make sure the brake shoes are not holding the drum on by loosening the star adjuster by going through the little hole in the hub. Set the hole at the 6 o'clock position and you can reach the adjuster. Then, if it is still stuck like mine was, I beat it with a hammer and it came off finally. You may have a threaded hole that you can insert a bolt into and force it off as well. Good luck.
