Jordan spreader air valve questions *PIC*

Looking for some help from experienced railroad shop guys who have worked on air valves used on MOW equipment. The attached and following pictures are of one of the control air valves on Jordan Spreader OU. Most of the hand valves leak badly according to the C&TS crews the last time it was used (there was also blow-by in the cylinders but that is another issue and is being addressed).
I have disassembled one of the smaller three-way valves and have not found that it is worn significantly. However, it does have a glaze of some sort on the brass surfaces and there is evidence of grease of some type that the valve may have been packed with (there is some sort of grease in the bottom packing nut that also has a tensioning spring in it). This grease is hardened and stiff and needs to be cleaned off and replaced. I am familiar with large natural gas hand valves that must greased in order to prevent leakage, but I would like to know if there is a specific grease used in this type of hand valve.
Any ideas, thoughts, guys?