The definition of a rule is  an official regulation, code of regulations or set practice. An example of a rule is that a red light means stop. An example of a rule is an employer demanding their employees arrive at 8am.
New injectors cost anywhere from $80-$120 apiece, making their replacement a somewhat pricey endeavor. There are three types of injector leaks-it can leak fuel into the manifold from the nozzle, it can leak fuel into the engine compartment from the fuel rail, and it can leak air (vacuum leak) from the manifold.
My injectors all run. I'm just concerned that one doesn't run well enough. I had planned mimicking the youtube video DIY Fuel injectors cleaning but after the Subaru dealership quoted the O-rings at $9.51/ea for a total of $76 I thought maybe a run of fuel injector cleaners would be in order. A 32oz bottle of Lucas Fuel Treatment will last for ~2100 miles and was only $12.