This problem has turned into a real head scratcher. Is it still leaking - even a little - anywhere that you can see? Air can go back into even a little leak easier than the fluid can come out. Assuming all of the gaskets and o-rings are also new, it has to be a connection. Offhand thinking it is one of the 'splice' connections going from the DF hose size to the master cylinder or slave fitting at the elbow is sucking air???
We can see this has been a very frustrating adventure, but hang in there. You will eventually find the culprit and get it fixed.