What action can I take against airline over loss of property

You can make a claim for the roller ball pen through UAL ticket process just as you would regularly. You may have to show proof of the pen purchase and get someone in charge to believe that your initial acceptance of the returned item was an honest omission about the pen on your part.

UAL has a pretty good reputation for luggage disputes here at the O'Hare International Airport, their home hub.

Good luck to you.

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