Yin,
The O-Ring doesn't come on it's own. Its all part of the PCV as per the pics.
Depending on which bit you need the breather line (plastic hose) part no. is - 06F 103 212 D
The PCV is - 06F 129 101 L
The Gasket is - 06F 103 483 E
Some pics
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HTH
Carl