Replace the shaft seal! And the clutch actuation arm seal if need be, while you have the cover off.
Get every bit of gasket material off using a putty knife. Then use some 400 grit paper to get the rest. Stick the gasket to the case with a bit of black high temp silicon. Oil the breather tube o-ring before installing. Put a small smear of grease on the clutch activator pin.
WATCH OUT FOR THE WAVE WASHER! Use a dab of grease to hold it on the shaft.
Photo credit to
http://www.dinqua.com/
