If the system is the same on the 72 300sel as it is on the 72 280se 4.5, it is highly unlikely that the seals are to blame for any visible fuel leakage as the seals are over a hole. It is more likely the fuel line clamp is just loose enough to allow fuel to seep down over the injector. I just had the same problem when I renewed the seals and with a slight twist of the screwdriver my problems were... well not over, it is an old mercedes after all...but no more fuel leak!