Rear Brake Master Cylinder parts

[txm123]

Hello, I’m trying to bleed the system and I can’t make it...It seams that one of the rubber seals that go in the internal piston rod is defective, really I don’t understand how does it work? I made a picture to show how does it look like. It’s very common in all the china motorcycles, especially in dirt bikes, I think maybe someone can tell me if I can buy new rubber seals or a new pump if this is the problem. I tried to pump 100 times and no pressure; I cleaned and disassembled the entire cylinder but no results. Thanks.