If you don't install the seal correctly, you will have a leak.
Axle Remove/Replacement:
1. Remove the axle nut.
2. Take the wheel off.
3. Unbolt the tie rod end.
4. Unbolt the sway bar link from the strut.
5. Unbolt the lower control arm from the knuckle.
6. Use a pry bar to pop the control arm out the knuckle, and move the knuckle to the side. (place bar under subframe and on top of the control arm)
7. Use a pry bar or large flat head to initially pop the axle out the transmission (wont pop if you have an old, useless circlip. and if it pops, it wont move out much just to note).
8. Pull the knuckle assembly with axle away and out from the transmission.
9. Place the end of the axle where it has room to move a good 8-12 inches back.
10. Place a small piece of wood on top of the axle stud, or use a mallet, and tap out the axle from the knuckle.
I usually use a hammer and pull the knuckle back as I hit the stud, and never damaged the threads in cases where I use the same axle again. You must hit it dead center though, and not give it a beating unless you want it to mushroom the head.
Install Reverse.