Check that the oil return duct of the turbocharger is not partially or fully obstructed by carbon deposits. Also check its thorough sealing.
Check, when re-assembling, that no foreign item does enter the exhaust manifold nor the turbocharger.
Apply high temperature paste on the screws/nuts on the area of the exhaust manifold / turbocharger.
Disconnect the negative battery terminal.
Check that the mating surfaces are clean and free from foreign items.
Use new self-locking screws / locknuts E.
.
Place back the components in reverse order of the removal.
Start the engine and keep it it idle running.
Check there are no leaks.