Ken, as for lubricant I mix 90 weight oil with corn head grease until I obtain a thick but pourable mixture. The fill plug is a good clue for you...GM intended the lubricant to be poured in and not forced in using a grease gun. The GM steering box lubricant was a bit thinner than fresh honey. To my knowledge it isn't sold any longer, though. The last I bought was in 1977. A lot of people claim they just use corn head grease but I believe it to be much too thick. You want something that is going to bathe your recirculating balls and all your steering box gears nicely and it must be self-leveling. If you turn corn head grease upside down, it won't pour out of the container. It is not self-leveling at all. I don't know that that little hole is...never noticed one before but I don't have a box from 1941.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end