[Jostes77]

How Common Is it to have the turbo go bad and at what mileage does it commonly occur

[TxGreaseMonkey]

Very common, especially if you don't use full synthetic heavy duty diesel engine oil. To answer your question, I'd say around 80,000 miles. My experience has been that if you don't use full synthetic HDDO, it's just a matter of time, not if, before the turbo fails--usually sooner than later.