I was seeing fuel around the High Pressure Pump Bleed Valve on my W30, 1979 Westerbeke.  Taking apart the fuel bleed valve I replaced the washer(s), fuel pressure switch and refitted.  The bleed valve is a modification to the standard high pressure pump on the W30 so the fuel pressure sensor can be used to supply dc voltage to the engine instruments when the fuel is of the correct pressure.  The sender is on the low pressure side of the High Pressure Pump.