I had a reservoir leak a couple years ago. Other than that it has been solid (swiftech), but there is no real way to tell in my system if it is running (no movement, and less noise than fans). It was not till I felt the CPU after shutdown that I realized that it was Fing hot. I moved the tubes around and saw a small bubble, turned on the computer and it did not move.. oops.
I think that when I rebuild I will put something in that lets me know it is running - a clear reservoir or one of these things...
Otherwise I will have to keep and eye out and do the Fonzie approach... (nice Ric)
cheers.