Just replaced mine, but the former had been going for over a year. Only died because of my stupidity. Did a large water change, unplugged everything in the sump (or so I thought), and drained most of the water.
Well, you guessed it, the heater was still plugged in, and was above the water line. Cracked and fell in. No damage done, only 2 pieces of glass, and no filament contamination in the water. I think it would have kept going for a while otherwise.