Hello Wolfgang.Excuse me for my rather poor english. I saw that tug boat about three years ago in a river vessel`s shipyard in the Escobar area . ( that is a small harbor on the shores of the Mitre channel, at the Paraná River delta, in Argentina.
I dont know if she is still there. Something you could try is to contact Prefectura Naval Argentina. You can visit the web page . May be they have data of her arriving to the shipyard or at least, the exact name of the shipyard. ( I'm not sure if the name which appears in the link you posted is correct.)If she was supposed to be converted to a yacht, probably she was registered at the R.E.Y ( Registro Especial de Yates ), the argentine yachts register which is ruled by Prefectura Naval.
In my opinion, her most probable fate is to have been converted to a pusher tug boat to be used for servicing the grain loaders situated up river and very probably under paraguayan flag.
As you see, this is not too much but perhaps, may be useful for you. Regards . Marce