Intercooler charge pipe O-ring/seal for plastic-ended IC, as these can often cause a boost leak or leak oil onto the undertray. Part numbers are for the latest green O-rings.
Seal A (one located at each end of the IC): 3C0145117H, corresponding metal retaining clip is 1J0145769H
Seal B (slightly smaller and located at the turbo end of the boost pipe on the IC inlet): 3C0145117F, corresponding metal retaining clip is 1J0145769B
To replace the full set, you need two of seal A and one seal B. I would recommend replacing the metal clips too as they can bend out of shape easily and are less than a pound each.