Unscrew the bezel. (My L600 makes a horrible grinding sound when I do that). Now look inside the barrel. You should be able to see the nipple of the 18650 cell on the bottom. See the stuff all around the nipple? It's a small, but noticeable amount of very tightly packed cardboard. (At least that's the case on my L600). At first, I thought it might be packing material that you're supposed to remove once you receive the light. But it doesn't come out. (I tried).
The serial number on my L600 is A00265.
One of the two O-rings at the tailcap snapped, recently. Not sure what was used to lube the light. I'm just hoping it wasn't petroleum-based. Couldn't find a similar sized O-ring. Ended up having to cut the other one free. Used a larger O-ring that doesn't fit inside the tailcap. Ironically, the oversized O-ring has caused the momentary switch to work far more smoothly than it used to.... Mostly because I can't screw down the tailcap all the way anymore. It now actually has room to move freely, and this has caused the switch to work better. I can still screw down the tailcap far enough for constant-on mode if I want to.
All I needed to fix the tailcap problem was.... the wrong sized O-ring. :huh2: