The splines on the axle can cut the seal. When installing the axle, first put some grease on the seal lip. Then wrap the splines in paper. A small note pad size will do. Push the splines through the seal with the paper wrapped around... just hold on to an edge of the paper so it doesn't go all the way in the axle. Once the splines are through, pull the paper out and insert axle the rest of the way carefully so you don't put a lot of pressure on the seal lip.

The only other tip is check the bore where the seal goes for any scratches from prior seal removal efforts. Thorough cleaning and a little dab of RTV on any scratches should prevent leaks there.