I pull down the wiper and clean it with wd40, rinse and work it around the fork tube several times til clean. I work it around in an eliptical way so it works the dirt out.
Then I go to the seal. I rinse it out externally the same way, several times, pump forks and do it again til it comes out dirt free. It takes a little work to get all the dirt out of the area.
Then once it is externally clean I do the sealing surface of the seal. I use a piece of plastic soda bottle that is cut with about a 1/4" radius to do the cleaning. It has a curve built into the plastic that helps conform and it is thicker and tougher than the commercially sold plastic piece. I bent the one I bought the first time I used it and then went to the soda bottle. Lasts for years.
Work it around a couple of times and then pump the forks. Do it again. Do it again. Put back together.
With this method I have only had to replace a couple of seals. If you cant find a gouge or ruff spot on the chrome part of the tube then the seal is PROBLY Ok.