I have seen quite a lot of these - best way is to apply some silicone grease on the O ring and make sure the clip is oriented correctly. it can walk sideways and cause it to not catch one side.

My first time with these I was running in circles until I rotated the clip properly so it engaged both nubs - use a dentist mirror to help.

Same with the top radiator hose, its clip can also not lock if it was disturbed. Make sure check if its in the right orientation. The factory sometimes uses a green paint marker to where the clip pulling loop is supposed to face.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)