if your fork seals are shot then you would see oil on your fork legs. If you used to see oil and don't anymore, then you are totally out of fork oil and are doing damage to the forks. Valves need to be adjusted at 26000 miles. Normal cost of around 300 bucks. That doesn't include the routine oil change/plugs,etc. As a fork ages, its gets softer because the fork oil loses viscosity. With 20,000 miles on the bike, the fork fluid is probably totally shot. This would give you a mushy feeling and allow the fork to bottom out. You may be able to fix it by dialing in some more compression damping, however its probably time to have your forks service. If you want to replace the seals, expect around 300 bucks if you bring them the bike. If you just want fluid changed, it can be done on the bike and should be able to be done for around 150.