Given the design of a turbocharger and the fact that the rotating assembly floats on a layer of oil, the actual failure rate of a turbocharger failing without outside influence is approx 2%.
The biggest cause of turbocharger failure is lack of oil, with most oil issues being down to the oil feed pipe. In most cases, the oil feed pipe is a flexible steel braided over rubber pipe. Over time, the oil feed pipe collects carbon build-up and can also crack and perish due to the heat cycles and general age. This in turn restricts the quantity of oil entering the unit, starving it of oil. We, at Turbo Rebuild, feel an oil feed pipe should be renewed every 25,000 miles to ensure good flow to your turbocharger and trouble free motoring and MUST be replaced when any work is carried out with your unit.
There are of course many other reasons for turbocharger issues, below is a handy chart to help self diagnose your issue: