Hi , I have a Audi Cabriolet 1999 B4 1800 petrol. Does anyone know what the correct pump it is for this ? I have been sent one , but there is now a problem that when its driven the power steering is ok BUT when you apply brakes to slow for " roundabout/turn " the power steering goes hard as though NO power steering . Could anoyone shed some light , have been told look at the sphere done .. ok . Filter ..done clear !! Thanks