i had the same problem..turned out it was the matrix was blocked.the pipes are connected under the bonnet,two together.they can be removed but sometimes this does damage the seals,make sure you dont let the garage tell you that the seals are gone and they have to replace the matrix,this is not so[but its a good earner]...you can obtain these seals from the main dealer,just remember this.good luck.
eddie, December 2006