Updating for those who will find this post latter:
I lubed the stabs. And rattling is mostly gone. But left side of spacebar is still a bit more loose than the left one (I feel it by lightly touching each side - at the left it chatter a bit). When I took the keycap of it seemed that stem in the left stabilizer was sitting deeper in on the right.
Honestly I am disappointed after reading all those odes to Leopold quality. Niz keybaord which I bought few weeks ago doesn't have this problem at all.
On the other hand, it costs 130 Euro which is on pare with other keyboards like Filco, Das, Varmilio and so on - why should it be any better.
I think I will keep it as I lubed the stabilizers already, but I don't have that feeling of satisfaction I expected to have - more like wasted 130 euro...
Bought form candykeys.com