The air-cooled RDs have on the left side of engine a screw for adjusting the clutch clearance. If there is no clearance, all clearance at the clutch lever useless. While mounting the left
engine cover you can notice missing clearance. Then the cover totters over the clutch push rod back and forth.
This screw is mostly never used. At all my air cooler RDs this screw was so tight that it could only be resolved in a vise.
The current high-performance gear oils do not fit to a wet clutch. Use 10W-40 4T Shell Advance VSX oil.
Is the clutch still slipping put under two of the six clutch bolts an additional 2mm washer. This increases the preload of the spings.