Savoia:
I don't have any hard data, but I can tell you something from an accident that I worked on in Romania in the early 90's that involved an Alouette III. Turbomeca told the Romanian authorities that aside from someone not servicing the engine properly with oil, or running out of fuel that they had had no more than two engine failures reported on the Astazou model.
The UK CAA at one point about the same era had stats that showed the failure rate of Turbomeca engines was 1/20th of another popular model, and I'm sure the numbers in favor of Turbomeca were heavily skewed because of the Astazou (there being few other engines of their manufacture at the time).
But no hard numbers that I'm aware of.
And some of the reliability had to be at the price of fuel consumption - the Astazou was about 25% more thirsty than the competition for the same horsepower as I recall.