This is a procedure I found in another forum. Looks pretty good.
Here is link for pics: http://markb.smugmug.com/gallery/258410#10158717
1. Remove sprocket cover (3 6mm bolts, w/ 10mm heads)
2. Remove large keeper nut, washer and sprocket, and chain.
Usually you can pop the chain off the sprocket, and tuck the chain out of
the way against the swingarm. You'll need to flatten out the washer with a
punch and hammer. The large nut requires a 27mm hex socket, or you
can get by with a 1-1/16" socket.
3. The oil seal is inside the left half of the crankcase, but usually comes
out pretty easily. I bent a small screwdriver to use as a removal tool.
Pry on the front, then back, then top, then bottom, repeat, seal is out.
Place seal in discard pile.
4. On the countershaft, there will be a collar. Remove the collar and
check to see that it is not excessively worn or grooved from the seal.
If it is worn you should replace it.
5. On the countershaft, behind the collar, there will also be an O-ring.
Remove the O-ring and set in the discard pile.
6. Clean the countershaft and the seal surfaces with WD40 and clean rags.
7. Install the new O-ring onto the base of the countershaft. I slipped it
into place with a small scrap of rolled paper acting as a sleeve.
8. Wipe the bore for the seal with clean oil, and install the oil seal with the
smooth side out. Press it into place with your thumbs. It should be FLUSH
with the surrounding case. NO gasket compound needed.
9. Dribble clean oil onto the collar, and install it onto the countershaft.
Be sure the notched end goes in first. Check the parts diagram to be sure.
10 Reinstall the sprocket and chain, and the cover. You'll need to bend the
tabs of the washer back up to hold the nut. Double check the chain
tension. I set it so that the chain just touches the swingarm, right under
the rubber chain slider (the little vertical strip w/ the screw in it)
There's a few pics of the process posted below. These are from the earlier
year bikes (1989 in the photos, the same except for the sprocket keeper)
Late model parts: I replace the O-ring and Seal when I'm in there, but
you'll want to double check the collar for wear, or the new seal will begin
leaking all too soon.
Oil seal 92049-1159
Check the fiche (buykawasaki.com) or your dealer to be certain on p/n.
ronayers.com or bikebandit can sell you the stuff online.