Problem:    Burrs hadn't been used for a while and collected moisture and started to rust 
Solution:   "Rust remover, scrubbing, washing, and coating in coffee oils" 
Brand:  Mazzer 
Cost new:   £50 
Cost of fix:    5p 
Age:    4yrs 
Success?:   Yes 

I got a new Mazzer Super Jolly grinder and it's one of the projects I'm doing to refurbish it up in the way I want to. Part of that included doing up the burrs as they had accumulated a bunch of rust and were dirty. Because they will grind the beans I didn't want rust on them. Used some rust remover and plenty of scrubbing with a nylon brush and some wire wool cleaned it up after a bunch of passes. Washed off the remaining rust remover with water, then popped them in the oven at a very low temp to make sure there was no remaining moisture on them. Then I ground a whole bag of cheap beans to a very fine grind to get them covered in some bean oils to protect the surface.