456 Brake box

Does anyone know how much a brake box will cost for a Ferrari 456? Its just behind the wheel on the drivers side, It leaks break fluid while I pump the breaks? What about a second hand one? Not too sure what the correct name is. According to Eurospares it maybe called a Two-Way-Union http://www.eurospares.co.uk/searchResult_one.asp?S=157719&TM=1&TMo=568&TA=1&TB=31293