Did you pull the residual pressure valve out of the master cylinder port that feeds the front disc brakes? If not do that and see if the dust gets a lot less The valve is capture by the brass seat in the master cylinder that the steel brake lines seat on, remove the line and use a #8 self tapping screw to screw into the brass seat and pull it out, remove the little rubber flapper residual pressure valve behind the seat and put the seat back in and tighten the steel nut up on the brake line as tight as you can get to make the seat reseal IHTHs