New rear callipers trouble bleeding

Just fitted new rear callipers and flexi hoses on my allroad 2007 3.0. I have bled the entire system and no air coming out at all now, but when I push the pedal with the engine running (so brake servo assisting) the pedal is not solid. It appears solid at first but slowly sinks under consistent foot pressure. I can not find any leaks, and have re-bled all 4 callipers a second time now, again with no air in the fluid, but the problem persists. Anyone any idea what to try next (besides taking it to a garage)?

Cheers, Paul

I was using the pressure bleeder kit from eurocarparts - its almost exactly the same as the Gunson Eezibleed - which is not a vacuum bleeder BTW - its a pressure bleeder which pressurises the fluid into the master cylinder reservior. The very first bleed I did was with the callipers not attached to the carriers, but holding them in hand whilst rotating the callipers in various orientations to get all the air to come out of the bleed valve. I then fitted the callipers properly to the carriers, with pads fitted etc. Bleeding again, fluid was flowing through nicely. Initially with air bubbles coming through the pipe (this was new callipers after all, so I expected to see a lot of air at first) - which seemed like it was coming through for ages, and I never thought it would stop, but then I then slowly pumped the pedal whilst it was bleeding, and the air soon went away, and I could see only clear fluid coming through. Same on the other rear brake and the same a second time (with no air coming through at all on this second round). I then bled the two front callipers. No air came out at all.

At no point during the calliper replacement has the fluid in the master cylinder run dry, so i do not imagine I would need to go through an ABS bleed (using VCDS), but I am open to suggestions on this front. As it stands, the car has been out of action for nearly 2 weeks (waiting for parts and tools etc) now and I'm getting a bit frustrated with it. It has cost me over £600 in parts and tools and the last thing I want to do is limp it to a garage for them to bleed it now.

I tried vcds - controller 03-ABS Brakes, Basic settings - 04, Group 001, and got "Error Group 001 Not Available".

I took the car for a run. It actually feels fine whilst driving, but that's because you don't generally drive with the foot hard planted on the brake checking for it to sink. It makes me wonder if the brake might have been like this prior to my calliper issue, and that the issue here might be something to do with the master cylinder rather than trapped air. I do not see any leaks at all from any of the brake pipes/hoses/components. Would be interested in your thoughts on this suggestion?

Since posting the above I found an article that suggested the correct group for ABS bleeding in vCDS is 002, and not 001 (which is only for Golf etc) So I just tried with the 002 group and again got the error "Error Group 002 Not Available". Anyone got experience doing this with VCDS on a C6? My VCDS is version 11.11 (so quite old). Also wondering how much brake fluid would be needed for doing the ABS bleed procedure - assuming I could get it to work with VCDS?

Guys, I'm really struggling with this and getting really desperate for some help. As I previously reported, in VCDS under the ABS Brake controller there is no option inside "Basic Settings - 03" for bleeding the ABS - I have only two options shown in the drop-down - one for steering sensor calibration and the other for ABS diags mode (these names rough guesses from memory). I found a video though which suggested an alternate method which I was able to carry out.
This method uses the "Output Tests - 03" option in the "03 - ABS Brakes" controller in VCDS. I followed the video as close as I was able. I used a pressure system instead of a vacuum system to force the fluid from the reservoir through the ABS and through to the front bleed valves. I kept the brake pedal depressed during the process using a block of wood pushed between the pedal and the front of the seat. Although the fluid flowed through the bleed pipes, I did not see any air come through at all. This suggests to me that the ABS block is OK.
So, can I assume from this that its likely the master cylinder? I would have though that it should be OK as the car has been fully serviced since new and the master cylinder (at least externally) looks like new still. Obviously I can't vouch for the internals.

One further question - trying to find which Bentley manual I should buy for this car - I was not able to locate any which specifically covers my late 2007 Allroad 233bhp. Can anyone please offer any suggestion/link?

Thanks in advance, Paul