[elmariachi]

I wouldn't say its Black Magic, but if you get it wrong, things can leak, wear and break and that can be dangerous and expensive. Search yahoo for "Ford 9" rebuild" or similar and you'll find plenty of detailed how-to websites. You need the right tools, including lots of compressed air to remove the pinion nut, a good torque wrench, a dial indicator and dye/marking ink to setup the tooth pattern. Its very straight-forward if you have a reference and the tools.