Philippe there is a third paradigm that I adhere to.Richard, I would let it as it.
There are two opposite opinions about how those old things have to look like.
Some collectors want to have them as they were, shiny and clean. Other collectors do not want to change anything from the old patina, because this is a part of the helmets story too...And this mostly is the proof that the helmet is still untouched and that nothing on ist has been moved on or off, or manipulated at some time.
Philippe
Everything gets a thorough dusting with a vacuum. Just to clean out decades of post-war dust and tiny dead animals.