Axle seals are a piece of cake to replace. But, as you say, it's very easy to nick the seal seat. When I replaced em, I used a screwdriver with a shop towel over the tip.

Oh, and when you put the seal in, don't drive it all the way against the seat. It'll leak if you do that. What you wanna do is, drive the seal in about a third of the way. Then install the axle. The axle will seat the seal itself.