After two weeks of usage, my servo started jamming at one side, and not going back to center.
Long story short, I found the solution.
The root of a problem is a small gaps between contact pads. I've marked them yellow on the attached picture. After intensive rotation copper smeared between two pads, and they become short circuited.
Solution is very simple - clean the gap with knife or so.
Of course if I was able to send my servo to LEGO I'd rather do that.