A common mistake a lot of folks make when they redo their O-rings, is they do not get the caps back on properly. A good rule of thumb is this.... the injector line nut should NEVER touch the return cap. If it does, you don't have it pressed on all the way. Also, once they are correctly installed, you should NEVER disturb them. Heat and vibration sets them up such that once they have been in place for a while, if you bump them, or otherwise look at them funny, they will start leaking. Consequently, when you repair one of them, you have to repair them all, because it's damn near impossible to replace one without disturbing the one next to it, and so it goes like dominoes.