You are correct, 1940 3/4 ton specials are semi-floating and almost identical to the 1/2 ton axles. The same axle seal and similar bearing is used from at least 1939 through 42 1/2 and 3/4 ton and 1/2 ton through 1962. You will find the axle seal available through most of the venders that advertise and support this site. I don't see them listed at NAPA. Not cheap, usually around $25 each. You may also check to see if the toque tube seal is leaking, letting excessive transmission fluid leak into the differential housing and overfilling it.
