Frankly, the LocTite on the set-screw seems to be, and probably is, sufficient to ensure that the clutch arm doesn't vibrate loose. Not to mention the fact that once you know what's happened you can literally prop something behind your clutch pedal and then reach under the car from the driver's side and put the arm back on by feel and carefully limp home should it happen to you. That being said I did add this last bit of safety margin. It's simply a 1-1/4" fender washer with a dab of J-B Weld on the spline and washer-hole. Now if I need to remove the clutch arm sometime in the future I will have to whack this off with a screwdriver and mallet, but this will hold the arm securely should the set-screw manage to vibrate out past the LocTite.
