Its not the bearings that have an issue with the lubricant in the steering box. Its the sector and worm. The pressure between them when the wheels are turned will push regular grease out and leave the 2 parts metal to metal. It will cause galling. It is well pointed out that gear cases and parts that are under extreme pressures need specialized lubricants. I'm not saying that people haven't got years of service out of using home brewed stuff or just plain chassis grease, but consider that most of these old trucks we have don't get many miles a year put on them. If anyone is interested Google gear case lubricants and read up on the requirements for them.
