Mine was not sealed, which measn presumably that is was tampered with before I bought the bike. This is an excerpt from the manual which implies that it should be adjustable to get the correct freeplay.
The lever screw is not a user adjustment. It is set at the factory to obtain the proper piston stroke volume and correct bleed-back rate. Leave it alone.
A worn clutch is most easily diagnosed by cracking the throttle open in top gear. You'll feel it slip when the revs rise.