without probing the box thru the fill hole.. or pulling a side cover a tad.. you can only guess.
if you put grease in it.. ise a 0 or 00 ep grease. in 62 ford decided that was a better idea for those older steering boxes, seals.. etc.
your call. if the seals were tight and diameters good.. sh'll hold oil... if a lil loose.. then thin flowable grease is a good fill.
ps.. if it leaks at that cover.. might be a bad oring