Its an easy at home rebuild. However, the replacement part is the nozzle when you do a rebuild and im not sure a bad nozzle would cause a leak there. My advice would be to pull the injector, take it apart and clean it. Then reassemble and make sure you screw the 2 sections together nice and tight. Reinstall and look for leaks. One other possibility is that you have a crack in the return line nipple that is leaking down into the area where the 2 parts meet making it hard to tell where the leak is. Im sure you will find out once you pull the injector.