He's got a '40 GMC Panel . and he has a problem ?!?
Sounds like the spring carrier locating bit on the axle housing (that is rivited on) is loose and allowing the diff oil to leak out .
Or as Luke says , the axle casing may be worn thru and leaking ( same place).
I have fixed both problems , but really it is MUCH easier just to change out the axle housing for one in good condition.
