If you find that your hubs need oil, most likely you will
need new seals which are on the inside part of the wheel hub.
The repair kit contains a new seal and a ring upon which the
seal seats. The seal is installed in the hub and rotates. The
ring fits on the axle with a tight fit so that it does not
rotate. Unless you know that it is there one would think the
ring is part of the axle. A pry bar type of tool is used to
remove the old ring and the new one can be installed by using a
brass mallet and/or the old ring to gently drive it in place. Jerry Whiteaker 11/10/08
The drive axle is a different beast, only the front axle and tag axle will have these fill ports since in those areas all that is turning is the wheel. The drive axle will have a shaft that goes back to the differential. The axle, differential etc is filled with lubricant. So if you have a leak there, I believe you need to drain the differential, undo the hub bolts, replace the seals, refill the differential and that will not be measured in ounces of oil. When you pull off the rear top hat see if you can determine where the oil came from.
The hubs should use 85W gear oil, you can find it anywhere including Walmart. Just remove your front hub caps and tag axle top hats (pull off the decorative lug caps and the rest will come right off). Once done you will see a red cap, its a rubber plug and will pull right out. Add in the gear oil until you are at the full line and put the plug back in.Steve Cook 2003 U320 40'
Bearing Oil Change interval - James Triana says to leave it alone unless it turns milky or is no longer transparent.
Inspect Steer Axle Hub Oil