I've turned the nut counter c/w so far that I felt it was completely loose then I turned it approx 1/6 turn c/w just to let it grip again. Then I left the bass leaning against a wall to help it regain a bow for 48 hours - didn't help...
Anyway, thanx a lot for You trying to help!!
/p.
...and this is why I'm thinkin' of unmounting the neck and fix it in some kind of home-made pressure-stand for a couple of days.