It would appear my problem is not to do with bleeding at all but rather a leak from the rear port on the master cylinder.
Does this look like it's "in" all the way to you guys? I am reluctant to keep tightening it. I don't have a torque wrench that can go on a fitting like this.
BMW TIS says this fitting "Brake lines to hydraulic control unit" should be 17 nM
https://www.newtis.info/tisv2/a/en/e...-lines/5eAqjtl
I don't really think I can tighten this thing anymore...