do i need to reduce the fuel pump voltage from 12 to 6 volts?

Are you saying fuel line connections at the filter leak? Are they the banjo type? drilled bolts with copper washers? If so, they must have new washers and the proper procedure and assembly as well as torque. feeling it tighten without exceeding the max torque too bad should seal them. Those hollow bolts are sensitive to being snapped, careful assembly and attention to detail is a must. new washers are used every time. Bosch fuel filters always have them supplied.