2.0 Tsi vRS clutch issue

Hi all, I've got an issue with my Octy, 2012 vrs petrol. It's done 43k miles only had it since last December. Few weeks ago clutch pedal started feeling strange and eventually went completely, I knew the master cylinders were common failures so I've had that replaced, but still no pedal, after bleeding the pedal would feel okay but once the engine was started it would just sink back to the floor again, now we have changed the rubber seals on the master cylinder and re-bled the system and it felt fine for about 8 miles, performed perfectly, but once I got back to the house reversing up the drive slowly (so clutch partially depressed) the pedal has gone again. Tried to bleed yet again but this time goes soft and sticks to floor even before starting the engine. If I lived somewhere normal this wouldn't be a huge problem but I live on a little island off the west coast of Scotland so I've limited options with regard to getting someone to look at it, a friend of mine is a qualified, competent mechanic at the local rocket range and hes been helping me with it but even he is at a loss as to what could be causing the ongoing issue. I'm loathed to get it transported to a garage to have the slave cylinder replaced as this is going to cost me a fortune by the time I factor in the job and logistics. Does anyone have experince of this issue or know anything we might have missed along the way? I am at my wits end with it, I'm lucky I've still got my trusty old 51 plate mk1 diesel or id be right up s***s  creek without a paddle!