Recoil-

I posted on this before and had great success using oxalic acid. The black stains are iron/steel oxidation, and oxalic acid is about the only way to get them out without removing the offending wood. Apply judiciously with a q-tip to affected areas. I only rinsed with cold tap water to neutralize it. I did not have any bleed over into non-affected areas or "over bleaching" of affected wood.

skatr2