The most common cause of leaks at the pumps are the copper crush seals on the fittings at the pumps. I suggest you get new crush seals for the fittings and the check valves on the pumps. The original seals between the check valves and the pumps are thick and tend to leak . The replacement seals will be thinner than the original seals. Be careful not to over tighten the cap nuts on the banjo fittings. I have seen many of these leak from being over tightened and deforming the banjo fittings.
Mercedes Benz Master Tech