I can tell you that the most likely reason for this is switching off the engine when the turbo is too hot. Though the turbo is water-cooled by engine coolant and the bearing is cooled by engine oil, if you regularly switch off when the turbo is near red hot, the coolant in it will be unable to cool it and the oil in the turbo bearing oil feed and oil return pipes will gradually carbonise, eventually blocking the pipes. So, after constant speed on the motorway, after a long ascent, or after towing, best to idle the engine for a minute or two before switching off so coolant and oil continue to circulate through the turbo, gradually bringing its temperature down. Having had a new turbo, you must ensure that the turbo bearing oil feed and oil return pipes were replaced or the new turbo won't last long.