title_body: Grinder reassembly: should I grease the gearbox?
upvoted_answer: Yes, I assume the gearbox was originally lubricated to function properly somehow. I cannot believe the gears just rotate by their own. 
  
  And about the sealing. Such devices produced in bulk mostly do not care about proper sealing, no worries. Therefore, some parts may get in contact with your food.
  
  Finally, about greasing... There are food-safe lubricants made out of vegetable oils for food machinery. These are generally aroma-free, so they won't affect the taste of your coffee. You can buy one of them and use. I don't link as you can easily search the net.