I copied the following info from a site a few years ago from a guy who professionally rebuilds steering gear.
The Proper Lubricant
Manufacturers used a special moly-based steering gear lubricant inside the steering box. It lubricates the mechanical actions of the box well, is thick enough to cling to parts without running off and settling to the bottom, and is soft enough to flow back and forth inside the box by the pumping action of the rack block and sector teeth. Heat from the exhaust manifold and engine will soften it on cold days and yet the grease stays thick enough not to liquify and seep out of the bottom seal. A good moly or lithium based chassis grease will work in this situation and is easy to find in tubes and install using a common cartridge-style grease gun..
Do not use a liquid lubricant (such as 90w axle fluid) in a steering box. Liquid lubricants will settle in the box and not lubricate the upper portions of the gears. It will also seep through the bearings and leak out the bottom seal. Do not use wheel bearing grease inside the box. Wheel bearing grease is too thick to coat and work properly. Wheel bearing grease is designed for the high heat enviroment of the brake system and does not soften with heat and will not flow through the box like a moly-based chassis lubricant will.
