for one the orings have nothin to do with the engine flooding they just keep the fuel from leaking out of the rail and plenum etc.
its where the solenoid is staying open which lets residual pressure push extra fuel into each cylinder.
normally from experience if its only one injector that played up replace it. but if all have played up either its a electrical issue or the ppl that cleaned ur injector did sumthing terribly wrong lol.