There is something about Molybdenum Disulphide that had a safety factor...maybe just because it's a powder and you don't want it in your lungs. Last place I worked got really uptight about it. They apparently lost certification for using it for a very specific critical industry and had to find a workaround.
I haven't greased a helicoid, but I have done folder lens front cells with a synthetic # 28...I just forgot if it was Shell or Mobil. Wide temperature range. Pretty burgundy wine color too.