I have a 04 silverado that has a brake leak. I have found where the leak is but not sure how to change this line out. I will try to attach a picture. It is located under the driverside door.

The leak appears to be coming from the rubber boot area that goes up into the body

 

they don't run hydraulic brake lines into the vehicle only the e brake cable...which is mechanical.
the hydraulic line is steel; in the picture with a drop of brake fluid falling of it...someone has spliced into the original line as there is a union present joining the old and newer lines.

have someone step on the brake while you view the line...or use a go pro...you will see it linking out of the metal line.