The yellow cap part is a fuel injector. So that is fuel that is leaking not coolant? And the metal part on the top is the fuel rail. You have to depressurize the fuel system, and remove it. There is an o-ring on the bottom that will need to be replaced. Replace the upper one as well. You have to remove the fuel rail to take it out, so all of them have to come out.
I'm seeing the thermostat housing in the lower right corner of the photo. If it really is a coolant leak it's going to be the thermostat housing gasket. Coolant is probably pooling under the fuel injector from the thermostat housing. HTH. -Jim
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