These are not easy to seal. Mine leak on the KH(A) and that has the rockers fed from the return rather than the pressure side.
You have followed the correct sequence for assembly though, haven't you? This is to slacken off (or even remove) the large head screws on the outer end of the rockers. Then you tighten up the nuts on the inner ends against the banjo with new copper washers. You can make up a tool to hold the rocker spindle from turning to make this easier. Let me know if you need the details and I will look it out. It is an invention of the late Ralph Hawkins. Finally, you tighten up the large head screws.
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.