what would cause an intermittent fuel leak at the engine

On top of the engine around the injectors replaced all injector seals did not leak.car set for a couple hours drove it and it started leaking again

On te center of the fuel rail is a round piece that is screwed into the fuel rail could it be that

Can't say.... Use the mirror and light to look!... It certainly could be the Fuel Pressure Regulator...

Where is the regulator located