Before you go replacing the seals, try this. Yank the forks off and change the fork oil. Before starting the process, take some camera film, or negatives, and run it on the inside of the seal (once you have taken the wipers off. Just work the film around the fork slowly getting the whole seal wiped. Now change the fork oil. I do this every 6 months.
When you are all done changing the oil, buy some fork booties from
www.holeshotktm.com. They will save you a lot of seal wear. Also, takes Scotts advice and bleed your forks after every ride. Bleed with no weight on the front wheel.
There is one more trick I want to share. You can trim the spring that goes around the wiper about 1/8 to 1/4" to snug up the wiper a little. To do this you remove the spring, by unscrewing the two end. Trim a small amount from the male (small) end of the spring and screw back together. All of these little tricks combined really saves on changing seals.
I too have a '99, and have never had to change seals (2700 miles including racing).