Hi as per my conversation with the tec he reckons that VAG changed their seal compound back in 2010 as they were getting too many warranty issues, the seals are a mixed compound using Neoprene to aid longevity but this is prone to a reaction with the other types of fluid on the market which is why they always demand you use manufacturer brake fluid, it wont cause the degradation, I did think at first that I was the only victim of this but then my daughters Q3 had the same problem within a year of having a new clutch both clutch master cylinder and slave cylinder were knackered, had a chat with the garage that had fitted the clutch and just slipped in what brake fluid do they use and they showed me a bottle of silver hook fluid, just about the cheapest universal yo can buy, got it back to mine and changed the master and slave cylinders, no small effort at my age even with the aid of the son in law, we bled the brake circuits as well with ESP4 and touch wood no problems for the last six months, gravity bleed in g is the best method once you have a pedal allow it to settle and just crack the slave cylinder bleed off with no pedal pressure and watch all the little bubbles come out they tend to congregate in the slave cylinder and then as air rises try and go back up the pipe towards the reservoir, I also got caught out by the radial seal in the slave cylinder and had gear oil leaking out of the bell housing which contaminated the driven plate so I had to buy a new plate Driven and Pressure, their other favourite leak is engine oil from the seal behind the ring gear, rear crank seal and thats a real mission as it has the crank sensor pick up attached to it.
Steve.