Clean it. Thats part of your braking system and even if it was operating correctly, that corrosion will find its way into the MC and clog a return hole. You might try Acetone or Kero or Diesel, any decent solvent that is aluminum compatible. Some 0000 steel wool and a gentle hand. Or, you could try some aluminum foil as the abrasive rag and a solvent.
But you've done such a thorough job, you owe it to yourself on the safety gear to not skimp.
