We have only had one turbo problem while our cars have been owned by us. About 5 years ago the Garrett T3 on my wife's 1986 745T was starting to rattle in its bearings when it was cold. I had the tubo overhauled and there was no housing damage. I do run synthetic oil because it is supposed to be better for the turbo.

I am the second owner of my 1987 745T. Th original owner had to replace the Mitsubishi turbo at about 80,xxx miles. The service records show an average of around 8,000 miles on oil changes, and at least once the car went over 11,000 miles without an oil change. You cannot properly maintain a turbocharger with such infrequent oil changes on dinosaur oil. My friend, Warren Bain (a regular contributor here) has a 1986 744T with about 295,000 mile and the car still has the original Garrett turbocharger.