Brakes goes spongy when engine on

[Corsa X10XE]

I have this problem with my Corsa. Its a T reg 1.4 with ABS. About a year ago or more I had changed one of the rear wheel cylinders and I think the brake linings were changed. After this the brakes were practically crap. Even though I bled it so man times with different methods, checked the one-way valve from the servo. I had even replace the master cylinder for a similar, but then realised one number was different. Got another with same numbers, but the ports were bigger. It made no difference. I even opened the original master cylinder to re-insert seals to make sure they were properly, but no cigar.
I have bled the car, using pressure bleeding, and manual. I think I had even bleed it once with the wheels off the ground as to the usual with it on the ground. I am left confused, has to be the most difficult car I have come across at bleeding. I can get the brakes solid by bleeding with the engine off, as soon as it is turned on and go for a drive, it just doesn't have the bite and creeps to the floor.
I was even looking at replacing the servo, but the ABS servo seems non existent for sale.

Has anyone come across this problem, any tips before I end up taking a sledge hammer to the car, lol.

[johnny]

Did you bleed them with the car running?

Sent from my SM-G900F

[Corsa X10XE]

Yeah I did this once, but it still didn't solve it sadly

Did you bleed them with the car running?

Sent from my SM-G900F

[johnny]

Are you starting at the back wheels, should do left rear right rear left front right front

Sent from my SM-G900F

[Corsa X10XE]

Are you starting at the back wheels, should do left rear right rear left front right front

Sent from my SM-G900F

Yes, I followed it in this exact order.

[stanc3w0rks]

Are you losing brake fluid?

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