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.
The fuel injectors that are in your BMW are more than adequate for stock engines, and supply more than enough fuel for maximum power and open throttle. For your engine to achieve maximum power, it must have a air/fuel ratio maintained within a certain range.