Dont do it. Those are a sealed bearing also, no need for gear oil .
Manual hubs do need grease, but dont over do it. The vacuum hubs do have some grease , and if you take them apart and they are dry you can put some grease in them, on the cogs and seal lip surfaces .
On a vacuum hub system, Putting 80/140 in them will not do much except contaminate the vacuum system, probably destroy the vacuum solenoid as the gear oil will eat it , and it will swell the hoses..eventually, and then they will collapse and malfunction as well.
The 2 way manual / auto hubs are just a combination of both designs. I have seen them on F series also. Just sayin. They also use grease...not gear oil.
Fact is stranger than Fiction