Once you clean the iron, heat it up to Warm and iron over a sheet of waxed paper. It will make the iron iron smoother. After the waxed paper, iron it on a paper towel to remove excess wax.
I'm guessing that the 'junk' on the sole plate is either spray starch or sizing, while the iron is warm, spray the plate with same, then use a non-scratching scrubber to remove the 'junk' residue. If that doesn't work, try Vinegar or Goop Off, but I'm pretty sure that the first method will work. (What else could it be?)
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