I had a new roof installed on my house several years ago and the Class A chimney for the boiler was replaced shortly thereafter since it was not up to code (too short and inadequate clearance to operating window). The light gray shingles on the downslope side of the chimney now have brown tinted stains and the contractor blames the dye in the heating oil Has anyone else run into this and found a way to remove the stains without damaging shingles?