Disc Break E46

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Dear SifusI ve a burning questions here:a) When you found out that your disc brake not that smooth (few lines and not that rough la..), do you change it?b) Can the disc be skimmed instead spending $$$$. Yes, safety comes first but have use previous cars never been told to change but mostly skimming is done.c) If change (front) what brand recommended? Ori $$/ OEM (if any, as not well verse in this matter) $$Appreciate if anyone can give some idea.Thanks