This particular handsome genius has had a google and found this.....
http://www.apianotuner.com/WaterDamage.htm
....but I would, firstly, find and ring around a couple of piano restorers/specilaist music shops in your area for advice on the matter and see what they suggest.
I think its best to leave to experts if you value your piano.
Hope you get the stain off, Mojo Jo Jo :0)



