I've gone to a Mercedes specific parts supplier and their drawing of the reservoir does not show the O-ring connector. Looking as well as I can on my XF it appears to be a short plastic hose to the pump with a square(?) clip which appears as if it might be difficult to remove. Is the O-ring inside? And how do I get the correct sized O-ring?

I'm leery of removing the reservoir without whatever it is I actually need for the direct connection to the pump. They're using Mercedes part numbers but that isn't going to help without that specific O-ring/clip.