I have a 1989 dodge dually and I have had a few leaky injectors, so I replaced all the copper pieces and the o ring on the top and none leak except #5. Don't know what it could be now. Any ideas?

 

Where is the leak coming from? you could have an injector body leaking. Clean off the injectors and lines with brake cleaner (let it dry) and start it and watch for fuel leak. Use a piece of paper or card board to check for injector lines leaking not your hand.