Fork advice...

you`ll need a seal driver for the fork seals else you will only end up knackering the new seals when you fit them..not sure what the oil quantity is but you could measure the oil from the non leaky fork & go from there & re-fil with a lighter weight fork oil...i notice from your pic that you are not running a lower fork protector?, you should fit some `seal savers` or kreiga do some for £25 they will keep the english mud away from your seals & will help prevent any stone chips to your lower fork legs which again will only knacker your seals..if your worried about fitting the seals etc just remove the legs & take them to a good bike shop, they should save you the time fannying about & will probably only cost £40 odd anyway...but before you do any of the above take an old credit card or similar (thin plastic ) & push the corner up through the seal (remove dust seal first & clean around the fork seal before you do this) about 1-2mm then slowly run it fully around the seal,( you may need to trim & modify a little) this should clean out any crud which is probbably making the seal weep..spray silicon on the fork leg & push up & down several times..wipe off the excess repeat again if nessessary..it has stopped a leaky seal for me in the past :cool:

An old peice of 35mm film also works well to slide underneath the seal. If a peice of grit is stuck in there, you can dislodge it. If the seal itself is damaged, the film strip/plastic card trick will not work.

On bikes with inverted forks, in my experience, the brake side seal is much more likely to fail. I think the brake disk itself flings gunk onto the fork leg.

As for stiffer fork springs, one cheap method is to cut a few coils off of your stock springs. This actually does increase the spring rate. You need to make sure not to cut off too many, as you don't want the spring to coil bind before the suspension bottoms out. Also, if you shorten the spring, you will need to increase the length of your preload spacer.

The typical KDX fork has too soft a spring and too much high speed compression damping. Fixing those things will make a vast improvement.

As for fork tuning, increasing the oil level will help stiffen the forks as they get closer to bottoming out, but not make much difference in the initial travel. Thicker oil will increase rebound damping, and thinner oil will reduce rebound damping.