This disassembly stops short. To do a complete troubleshooting & cleaning of corrosion, you may need to pry off the cap that says DO NOT REMOVE using a small flathead screwdriver. There will be corrosion underneath often especially if batteries got stuck in the tube. You can remove the bulb seat with its attached electrical connectors by allowing it to come out the bottom tube of the flashlight body. Be cautious because there is a silver connector tab that can fall out of it’s slot and will need to be replaced in correct position. To put the round bulb & connector seat back, it helps to push it back up the tube using the batteries behind it. Otherwise it tilts and gets stuck in the tube.

I’ve solved this twice . Drill a screw into the bottom of the battery. Then pull it out. I used a variation on this technique:

https://www.youtube.com/watch?v=3aZCns5y...

There was a lot of corrosion. You can remove the cap that says “DO NOT REMOVE” located under the headcap. Your breakdown instructions stop before that point. The flashlight wouldn’t work again until I did remove that DO NOT REMOVE cap and cleaned away all the corrosion using a q-tip soaked in vinegar. Use a small flathead screwdriver to gently pry off the DO NOT REMOVE cap. Underneath, you’ll see another black round piece that the bulb fits into plus the electrical connections. I shook it gently out the bottom of the flashlight for complete cleaning. Be sure to check the orientation of the silver connector tab. It can fall out and needs to be put back into the slot. To put back, it helps to use the batteries to push it back up the tube so it doesn’t tilt and get stuck. Once reassembled, it all worked 100% fine again.