My Arc LSHP-F (#1663) suddenly wouldn't turn off. It temporarily became a twisty since only by backing off the Kroll tail pack could I get it to turn off. I searched the ARC FAQ and found the DIY maintenance page. The problem turned out to be the body spring. It seemed to be caught on the plunger, but with the help of an eyeglasses screwdriver, as the instructions say, I got the the top of the spring to go beneath the plunger. Problem fixed! So I'd add a fourth symptom that can be caused by this spring: the light doesn't turn off.