if the misfire is audible and you can feel loss of power then its probably an injector issue. Otherwise it could be an EGR issue. If you suspect anything leaking, spray a bit of carb or throttle cleaner where you suspect the leak is (with the engine running). But be ready to douse flame in case anything catches fire (very low probability, not trying to scare you). This engine design shows one of the more sinister sides of Nissan. There’s no need to cover up spark plugs and injectors such that you can’t perform injector or plug test yourself without having to remove the intake manifold. But then again, when people don’t work on their cars they become specialized items to be worked on by “mechanics” only , and nobody’s the wiser.