If you find oil leaking from under the left side engine cover, it probably is due to a worn clutch push rod seal. These seals can be problematical, because the rod is partly exposed and gathers dirt and crud. Then when the clutch is activated, the dirty part of the rod is pushed through the seal, wearing it.

The seal is about $8, and is easy to change, BUT NEEDS A SPECIAL TECHNIQUE.  This is because it was designed to be installed when the engine is being assembled, and at such time it is put in place in the bottom half of the crankcase.  There is a small groove running around the bore in the crankcase where the seal fits, and a little rubber lip running around the outside diameter of the seal, which goes into this groove.  Then the top half of the crankcase is lowered onto the bottom half, and the lip on the seal goes into the groove in the bore on the top half.  But you will be pushing in the seal from the side into an assembled crankcase, and if you don't do what I explain hereunder, you will shear off the little rubber lip and the new seal will leak worse than the seal you removed.

 Procedure

(1) Put the bike on it’s center stand. You do not need to drain the oil.

(2) Remove the left side cover.  Be very careful that you do not lose the little ball inside the clutch actuating mechanism attached to the inside of the cover; this ball is what bears against the clutch push rod.  It will almost certainly drop out when you swing the cover away, and roll under the nearest car.

(3) Pull out the clutch push rod. Another ball may follow the rod, if it does remember to put it back before re-inserting the rod.

(4) Dig out the offending seal, use a screwdriver through the center hole to lever it out, do not force a screwdriver between the outside edge of the seal and the crankcase.

(5) Observe the groove in the bore for the seal lip.

(6) Preferably using a Dremel, grind a shallow chamfer around the edge of the clutch seal hole, making it as smooth as you can.  The chamfer must be big enough so that when you push in the seal the little rubber lip running around the outside diameter of the seal fits inside the chamfer.  If you do not make this chamfer, when you push in the new seal the crankcase edges will shear off the little rubber lip, and the new seal will leak badly. With the chamfer, the lip will compress undamaged into the seal material until it pops into place in the groove.

(7) Lightly grease the inside of the hole in the crankcase, and the outside of the seal. Push it gently into place till the lip on the seal goes into the groove on the crankcase. It will be recessed in approx 1/16" when properly seated, but look at the seal and the groove in the crankcase before you push it in to see how far it needs to go.

(8) Insert the push rod all the way.

(9) Retrieve the lost ball from under the car where it rolled, and push it into the clutch actuating mechanism, holding it there for assembly with a dab of grease.

(10) Button on the side cover.

(11) Test the clutch.  If it doesn't work, take off the side cover and put in the ball you forgot to replace in your excitement at having changed the seal successfully.