Yes, you can do it from above if it's the shifter boots or shifter plate gasket. Remove the plastic stuff around the shifter, then the shifter outer boot flange screws, then the inner boot (check for tears). Then you can access the bolts that hold the shifter plate on the tcase. The tcase breather is the rubber mushroom on that plate. 4wd shifter in 2hi and tranny in N when you remove the plate...

Not responsible for advice not taken...