oil level in forks

first off, if the leaking seal is on the brake side, you'd better get it fixed soon or stop riding until you get it fixed. Otherwise, you will have no front brake.

If it's on the opposite side, here's how to add fork oil:
put the bike on a good stand or crate. If needed, remove handlebar clamp bolts and move bars out of the way (mark position first with a black marker), careful not to damage cables/brake hose. loosen upper triple clamp pinch bolts. Loosen fork caps all the way. Using tie down or blocks, raise the front end up as far as you can. Insert something into the non-leaking fork to measure level from the top. Add 5 wt cartridge fork oil to leaking side as needed. Make sure you snug up fork caps (not too tight) first, then tighten pinch bolts (the pinch bolts can compress the fork tubes enough to prevent free movement of fork caps).

It could be very possible that the seal is dirty, but not ruined. Do a search to find a method to try to clean it.

here's how to clean dust seals.
bottom of fork is a rubber dust seal, it might have dirt stuck allowing forks to be leaking. take it off with small screwdriver
working the seal off,left to right or vice versa. with the seal slid down the fork leg, use brake cleaner to remove dirt. then
use an old film negative to form a loop and get inbetween the fork leg and dust seal. spray brake cleaner up into the fork seal and fork leg until clean. reasemble....this saves me time
between fork seal replacements. works for me.