Originally Posted by filip00

Thanks for the explanation.

Yeah, my symptoms were very weird. Before I concluded anything, I went to the Nissan specialist that's nearby and asked their opinion. They have a device to pressurize the brake system and basically push all the air out. The mechanic also explained that while you can do everything well yourself with the foot pedal, because of the ABS pump placement, it's possible that you still get some air trapped somewhere.
Anyhow, they pressurized it, used the oil that I still had at hand (Motul RBF660) and it was good. Master cylinder is fine, it was just some air trapped. They also noted, that it's very very rare for Z's brake cylinder to fail.