After practice at a muddy track one day, I found one of my fork seals bleeding. One of the old pro's showed me this trick.
Grab yourself some generic tear-offs (film negatives will also work) and cut the end off one of them with some scissors.
Remove the fork guard and place a flat screw driver between the edge of fork and the dust wiper and gently pry them apart sliding the dust wiper cover down.
Take the tear-off and slide it against the fork tube, in between the fork tube and seal.
After working it around the fork pull it out and you should see some small particles. Believe it or not those will cause your seals to leak badly. Repeat this several times and you should see less and less.
After, don't forget to also clean the dust wiper before replacing it. Put the dust wiper back on and try bouncing on the forks a little and take a look, it should be cleared up.
This won't help if your seals are worn out but, it may save you a trip to bike shop and the cost of replacing seals.
There is also a tool called Seal Mate designed specifically for this purpose if you don't want to use tear-offs or film negatives.
In addition you may want to use a neoprene fork seal protector. These ‘seal covers’ filter out and help prevent particles from reaching the seals and therefore reduce the need for cleaning and also extend the life of the seal.