How do you know the flex lines are good? Are you getting fluid through the flex lines? If not, the flex lines can collapse inside and you can't tell. I know. This happened to me once. Just go down the line from the master cylinder. Disconnect a line then try and bleed. If the fluid passes through, then you know that section is good. Go all of the way until you reach the calipers. I had to do that and that's how I found out the flex line was bad on one side. It would barely let any fluid through.
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