Don't worry about the leaves at this late stage, nothing will cure it and it won't affect your buds potency.
Just try to ignore it and observe your flowers for when they are ready to harvest and judging by the pictures, this won't be long.
Flushing with great amounts of water will just make things worse, as it will leach any remaining goodness out of the soil and will not help your plant at all at this late stage.
Wait until there are about 90% brown pistils, flush with three normal irrigations with plain water then harvest when there are about 95% brown pistils.
This will save most. if not all of the quality that your buds now possess.
Hope this helps, Organoman.