1. Remove gearbox.
2. Remove the three bolts securing the clutch release bearing guide bush and slide the guide bush off the input shaft, together with the O-ring.
3. Being careful, using a screwdriver, used as a lever, remove the sealing ring from the guide bush.
4. Check the condition of the surface of the gearbox input shaft mating with the sealing ring and if there are scratches or burrs, polish this surface or replace the input shaft.
5. Dip a new O-ring into the oil and install on the release bearing guide bush.
6. Install a new O-ring on the back of the guide bush.
7. Install the guide bush in place by sliding it over the input shaft.
8. Screw in the guide bush mounting bolts, tightening them to the required torque.
9. Install gearbox.