The winners and the solution. :)
If I see correctly 
Hive account@cryptastic was the first one with the correct solution in the main line, while 
Hive account@greatwolf made a nice overview about both winning lines depending on whites first move. Both did very well, congrats (I upvoted both) - the problem is solved. Here the overview:
- ... Nf5+.
And now:
a)
2 . Kg4 Bd1!
3 . Qxd1 Ne3+ (followed by Nxd1).
b)
2 . Kh5 Be8+
3 . Kg4 Bh5+!
4 . Kxh5 Ng3+
5 . Nxg3 and stalemate (draw).
End position:
RE: Chess problem 40 / Schachaufgabe 40