No gears again

The indicator rod on my bike's gear hub pulled out again -- with exactly the same symptoms -- about eight miles from home, and I had to cycle all the way back in top gear once more. I simply couldn't get it to screw back in, or at least on the couple of occasions that it seemed to have engaged, it promptly pulled out again as soon as any strain was placed on it. So the new axle key has lasted all of six months...

There has got to be something wrong. These hubs are supposed to be bomb-proof :-(