Gear selecter seal

There are 2 seals since there are 2 moving shafts in the same hole. Replacing the outer seal only may or may not stop a leak.
Replacing anything is easier done while standing (with the car on a lift ) than done while laying on your back under the car.
I mention this because those who responded didn't say what their work conditions were.
Valve body has a crowd of bolts through but only a handful are actually holding the valve body up. A service manual will show which bolts need to be removed to drop the valve body without separating it and loosing the check ball orientation.
Good luck