Grease for kitchen stove natural gas vavle??

Someone spilled milk on our countertop stove unit over where the flame controls are - the one that goes from off to low/medium/high by turing the control. Well it got into two of the controls and they would bearly move. So I took them apart and cleaned everything up however there is the slightest smell of natural gas. I noticed that some sort of grease was used inside the valve assembly [cone shaped plug with holes in it] to faciliate smooth twisting of the valve control and probably to help seal out the gas from escaping past it. What sort of grease should I use on those part when I assemble them again? Thanks for any help.
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