I would think it’s got to be the pump seal then. Loosen the belt and see if there is play in the pulley. Another issue I have seen is a crack in the reservoir. Usually where the low pressure line inserts. Regardless if you are certain the lines are good then I would replace the pump and reservoir.
I think you may be on to something here. Today when I started the car the pump was making a screeching sound that went away once it warmed up (yes, the fluid was full). I saw some droplets on the rubber hose going into the pump and on the metal one underneath. None of which looked like they were leaking from the connections. There was a more pronounced drip coming from the bottom of the pump but never thought it could be the pump itself leaking. I did replace this pump a couple years ago so i guess it's possible I got a bad one. Not looking forward to replacing it again.