The way you describe the pedal drop is already exactly what it feels like when one front back circuit is open to the atmosphere. You said that you let the air out with your NT510 or equivalent?

If you aren’t spraying fluid out the front or back circuit the air must be in the pre-charge pump or the ABS block


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2011 E70 • N55 (me)
2012 E70 • N63 (wife)