w124 220te sls accumulator union

[garyexcel]

Hi have had major leak on the pipe from accumulator(sphere) went to change the pipe but how do you undo the union on the accumulator manual says to use open box spanner but the top of the union is a smooth taper with no flats the center is a recessed hole with no flats or points so how do you release the union. By the way it is an estate / wagon

Thanks Gary