Master Cylinder Question

[nyko46]

I just change my MB 1984 300 SD master cylinder but I did not bleed it on bench. Instead I try to bleed in the car after installed.
With brake lines disconnected I had someone inside of the car pressing the brake pedal while I was with two of those three line output from master cylinder plugged and trying to get one completely bleed
I used my tomb to plug while brake pedal was traveling up and unplug while traveling down. There was suction when pedal was traveling up but not pressure when traveling down. I tried it many times, I wait for the fluid get inside of the cylinder but everything was unsuccessful.
What can be wrong or what should I do?
The master cylinder was bought as rebuilt unit a long ago and only now I got it installed. I am also trying to find a seal kit to repair the old master cylinder removed but it seems to be a online hard to find part. If you know some place to find please let me know.

Thanks for your help.
Nyck