A lot of people like the stains as they give a tool character
If you really want to get rid of them I would try to buff them out using Brasso if not try T-cut for polishing cars,
(You can try the above with some fine wire wool or wire wool and some oil)
Depending on how deep the staining is you might have to get the Dremal out with a polishing mop on the end,
Someone will be along shortly with some other ideas
