This is a know issue, and there is some posts written on this prior. But to summarize, the Kroll switch will sometimes flicker when the button is not being pressed. This is typically a contact issue with the body spring. A quick remedy is to loosen the switch (by tightly grabbing the rubber boot and twisting counter clockwise) and then re-tighten it. This can be done with the light on or off as long as you do not completely remove the switch. Usually only a half turn is required. Do not over tighten the switch as the threads may be stripped.
A more complete fix is to remove the switch and clean the body spring. The switch must be turned off before removing it as not doing so may cause the spring to bind. The body spring is found on the side of the switch and compresses along the length of the switch.
Generally, we have found these switches to last a good amount of time with occasional adjustment or cleaning.
Let me know what your experience is.
Peter