In the past there have been a few questions about this so I thought I would share. King uses a special proprietary grease on their rear hubs, they say to never use any other type of grease but a synthetic 20WT oil can be used in its place. Last weekend I serviced my hub and used oil instead of the grease. I found the hub to rotate better and seemed quieter. I checked with King to make sure I could run this setup long term and here is there response.
I plan to keep using the oil just because it makes servicing it easier. Much quicker to do an oil change than it is to degrease the inside and relube.