Hello. Picture sort of shows the brown spots. Not sure what it is on these electrical plug contacts. I think it came from the device being connected to an old surge protector, so they may be a burn or oxidation. This one comes up from the middle but most of the other brown spots are just that (and I mean multiple plugs have at least one). This is probably the worst of it, but was wondering if anyone has suggestion on how to clean or remove the marking(s). I know that brass does not seem to be strong enough to brush it off. If any other pictures are needed, I'll add them. At the moment it is hard to capture an image properly. Edit: Changed original image to reflect better view. Also I don't think they are deep scratches, as the surface is smooth on the brown areas. Thanks for any input.