What is high pressure overflow on radiator

there is a 1" or so plastic elbow at the end of an about 1/2" hose that comes from the overflow tank and goes into the top of the plastic part of the
radiator. this appears to be called a high pressure relieve. There appear to be two clips (from radiator) that hold on to this elbow. Can this part be repaired? seems a difficult item to remove/check. I assume there is a o-ring inside .... sure hope it's not my rad.

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