1KO 615 273A is the part number I found for the bleed nipple but think that’s just the fronts maybe I’m wrong and they use the same part for the rears to.
Car went in for a mot and he showed me under the ramp the nipple leaking, the brakes had felt slightly off for a while as well, he loosened the nipple off and tightened it back up again and it did stop the leak and the brakes felt great for a few weeks a nice firm pedal but I noticed yesterday they are getting spongy again , he suggested replacing the nipple.
Cars coming up for a brake fluid change anyway so should probably replace all nipples if I can find the rears.