An H20 is a homeowner machine. I doubt if you have worn the clutch out. I think it is an adjustment problem. I wouldn't disassemble it.

Do you have the proper "thin" 1" open end wrench to adjust the clutch? Without either a commercial wrench or a ground down modified one you cannot properly adjust the clutch. I bought a Snappy, but it cost me almost $30. Worth it because it's 1" on one end and 15/16" on the other, so I can do Cooper Klipper and King O'Lawn with the small end.

If you still can't get it adjusted correctly, suggest you see a dealership, and ask them if you can watch the first time. Usually mower mechanics are reasonably helpful if you are paying them for the work the first time around.

Bear in mind that when you adjust the reel clutch, it will also affect the setting of the drive clutch. You may have to go back and forth to both clutches to get it where you want. Personally I like the reel a little "looser" so the lever goes past the detent and locks the clutch "on". I then set the drive clutch a little tighter, and only use thumb pressure to move the machine.