My first guess is axle seal but I've never been in a 3/4 ton axle. It doesn't seem to be from the wheel cyl. I just did the axle seals in my 65 El Camino. My guess is this would be much different if so.
Appear to be a leaking axle seal... Stick your finger in it and smell it. Gear lube has that "unique" smell.....
the oil was so old and full of dirt it was hard to tell. For now just cleaning it and will check later. Thx for the help