I'm currently trying to prep front brake systems for rebuild. I've gone through the Mc and the bore looks smooth but I'll probably smooth it a little more just to be sure. But it seems to have some gunk that is giving me a lot of trouble. This white residue inside the m/c itself will not go away. I've soaked it twice in carb dip, twice in purple power and scrubbed it multiple times with a tooth brush and a nylon brush on a impact. I always rinse with brakeleen. Another thing I'm wondering about is what this rust colored stuff is on the edge of the bore. I didn't think aluminum would rust so it must just be some form of corrosion but it's a pain to remove. Does anyone have any tips for removing the gunk from the sight glass window as well?