My first unit in the Army, we had probably 3-5 M4s that the finish was gone on the upper and lower receiver (only the receivers, not barrel, stock, etc). I asked the armor what happened and he said some Soldiers were using shaving cream to clean their weapons and no one realized it until it was too late. I can't confirm with first hand knowledge that it's true, but the armorer was a stand-up guy who I trusted and I always accepted it as fact.
Lots of threads on it:
Nah. He's been active.Looks like Elvis has left the building...