ah dude, like i said, it'll be delicate la, you CAN take a fine grit sandpaper and VERY VERY VERY gently work your way down, but be VERY careful with it, occasionally use some wd40 or something to wipe what you've sanded.
oxidisation is kinda like rust la, causes the metal to change from its shiny colour to the matte looking dull kinda finish, as for your allen nuts, i'd say get new ones dude, you dont want to run the risk of not being able to remove them later on.