That's what I'm thinking, pretty sure I damaged the seals on the new master, so need to start again.From your explanation, I will say again it sounds like the master is bypassing.
You say you can pump them up and get a strong pedal and hold it and it then it sinks under constant pressure ?? But you are NOT loosing fluid anywhere ?
Sounds like a bad master.
(Almost impossible to tell for sure without being there and seeing for myself - but that is my opinion as a master mechanic for more years than I got fingers and toes !! lol. )