I just wanted to know if it was possible to replace one leaky fuel injector and not have to do the entire rail, and does it have to be the same brand of fuel injector
My car has 170000 miles.
My car has an automatic transmission.
Yes, on this model BMW you can replace one injector individually relatively inexpensively. If you are able to afford it and are fairly certain it is an injector problem, I would suggest replacing them all at the same time while you are at it. Often times, when one injector goes bad, it is only a matter of time before another one fails. This should also ensure consistent operation among all of them. If you do only replace one at a time, I would suggest making sure you are using the same brands. If you would like to have this done, consider YourMechanic, as a certified technician can come to your home or office to replace the injector(s) for you.