No, you don’t ever need to refill liquid or service the closed loop part of Dell oem AIO.  The refill conversation refers to permeable transparent plastic tubing of custom open loop liquid cooler, not AIO. Typically what wears out and breaks first is liquid pump itself, but that would take 10+ years of continuous use. 
I have one of these Alienware Cryo-tech Edition CPU Liquid Cooling systems. I have a question that I never even thought of when buying the computer, do I have to refill the cooling system? I saw that liquid cooling systems need to be refilled about once a year. But I have no idea if this applies to my cooling system or not?
Aurora R13, liquid cooling, do I need to refill it?