Funnel King E-Z Flow Pour Spout with Tethered Drip-Control Cap, 1 Inch OD, Chemical Resistant, for Quart and Gallon Containers (32177)

It seems you've already been given your answer. So when you go to do this service yourself, based on the condition of the plugs in your photos, replace the sealing washers when you do it just to be safe. something like this to fill the fluid