I had my steering box rebuilt and they told me to use 90 weight gear oil, which I did. It has never leaked a drop since. If you look at the seal, the lip doesn't allow for much sideways movement or misalignment. Thus the bushings have to be accurately honed on installation. Some of the rebuilders will use a chroming process on the end of the shaft to bring the seal surface back to standard.
I would be concerned about a "catch" in the steering. If it doesn't go away with more lube, you have a problem with a vital part.
