I had the same problem with mine, bled in twice the 'old fashioned' way, to no avail. I also expected the master cylinder to be at fault but decided to use a hydraulic brake bleeder first.There just isn't any resistance on the pedal, its very soft, and lacks any 'feel'. With ignition off the brake pedal goes hard, but not rock solid.
This is what i used - http://www.ebay.co.uk/itm/Gunson-G4...173?pt=LH_DefaultDomain_3&hash=item53e6c97205
I pressurized it with 1 bar pressure or 100 kpa. I was very surprised how much air was in the system, I did both sides on the front calipers a couple of times as well as the rear to make sure all the air was out.
The brakes are prefect now :thumbs: