If that old faucet sillcock won't stop leaking and you've already replaced the seals, the entire assembly probably needs to be replaced. Faucets wear out over time. A faucet sillcock has a spout and handle that can be seen on the outside of a building. The shaft of the faucet goes through the wall and connects to the internal plumbing with a threaded nut. Screws hold a flange on the faucet sillcock to the outside of the building.
Turn off the water source that feeds the sillcock. There is usually a handle located on the internal plumbing that shuts this water off.
Turn the handle of the sillcock on to allow the water in the pipe to drain out.
Set a catch bucket beneath the nut that holds the sillcock to the internal plumbing pipe.
Place a crescent wrench on the nut that holds the sillcock to the internal plumbing pipe. The screws on the outside flange will keep the sillcock from twisting as you undo the nut.
Remove the screws from the flange that holds the sillcock to the building.
Pull the sillcock out of the wall.