When you put the new stuff in, including the new seals, make sure all the surfaces are clean and smooth.
Of course, a new axle will be smooth, but it might also have some coatings that have captured some grit. Makes cleaning it beforehand with some light solvent or just some oil or whatever you have around, a generally good practice.
With almost any new part!
And if the area surrounding the seal show any signs of abuse, such as nicks and even light scratches, add a tiny layer of silicone sealer around the perimeter of the new seal.
The seals usually come with some already adhered to the outside shell, but a little insurance from doing it again is a good practice too.
You should not need it, but you never know. I didn't think mine needed it and it leaked! In my case I did not remove the seal and put a new one in, I simply cleaned it off and applied a bead of silicone sealer around the edge.
Worked like a champ after that.
Always apply a tiny bit of oil to the axle shaft before you install it too, to give things a chance to slide and spin freely as they pass over the new seal.
You can apply it to the seal, or the axle shaft. Your choice, but even if I put it on the seal I still put a little on the shaft where the seal runs on it.
Paul