Little annoyed with tuning key

So I was playing my bass and the E string kept going out of tune. Looking a bit closer, and when I loosened the string the barrel turned, but when tightening it did not move. Bit odd I thought, so I removed the string and had a look and the barrel came out in my hand. It had sheered through!
Now I don't over-tighten the string so can't understand it. Has it happened to anyone else?

I have decided to replace all the tuners, and are going for Gotoh GB350 Res-o-lite.
I also decided I might as well replace all the strings at the same time, and am going for D'Addario NYXL.