Interesting! My oldest 4F was purchased and used back in the early 1980s, perhaps even earlier. As you say, easy to deploy, 360 degree visibility, and tough. The other two are more than fifteen years old.

I did purchase adapters and they now run on two lithium CR123s, replacing the original mercury battery, which still flashed the strobe, even though it was long out of date.

Sorry to hear the issues with durability and reliability. I am a bit surprised, because my "adapter" is nothing more than an assembly that lengthens the battery cavity to accommodate the cr123s. It looks pretty sturdy. How could anything go wrong, go wrong, go wrong......