If you're refering to my shortcut , it wasn't my idea. I worked with some seasoned old schoolers.
You'll need a target to drill the pilot hole. Lay a flat washer with a very small hole on top of the seal/case and use a flash light or pen lazer from underneath and mark your target.
If your car has a/c the underdash vent assembly will need to come out so the holesaw and angled drull will fit. Find a socket that fits inside the old seal . Stack 3 pieces new seal, old seal, socket and tape the together with a round of duct tape like ][_0----. Leave the starting edge of your new seal exposed. The trans case will peel the tape off as the seal goes in.