Originally Posted by JonathanJ

You can get the bottom copper washer and the top rubber seal separate , so if you can hear it leaking at the borrom or it is leaking oil at the top you are ok , but if leaking diesel internally then you have a problem , it is sealed unit and cannot do anything other than replace injector , Also note that the delivery pipe is " one shot " unit so you should really replace that at the same time when refitting injector .