Replaced my bleeder block valve with one from ECS. I think the OEM rubber oring shrank causing it to slip off and cause the clutch fluid leak. The left oring looks smaller? That was on the transmission side where the leak was happening. Car is 8 years old; did the delay valve removal when I got the car. New clutch 3 years ago. Looking at ECS installation manual the Mk5/6 (and I assume 7) has a "separate" compartment for the clutch/brake fluid. When doing a brake flush I assume the clutch side does not get flushed since it's separated. Could this cause deterioration of the rubber? Fluid from the bleed was pretty dark.
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So i tried using a high flow bleeder block with a stainless steel line and they did not work together: so the 4 o rings (2 on each side) only worked with the factory bleeder block and/or the stock line with the aftermarket bleeder block.. ended up with using the stainless steel line from the firewall down to the stock bleeder block and i have No issues with my stage 3 endurance. The aftermarket one is just sitting in my garage somewhere .. Not really relevant to what your asking but sharing my experience