Turbo problems on the Dci engine is *VERY* well known about.

Nissan have been replacing turbo's as and when they fail, FOC, and also
checking the ECU is running the latest software which runs the turbo at less
than orginal boost (to make life easier for it) but which also has the
effect that power and torque are reduced soemwhat.

Allowing extra cooling off time after a high boost run has apparently been
helping abit, as does more frequent oil changes, however the turbo is
guarenteed to fail sometime before 50k miles, if not once, but twice.

Tim..