Turbo charger Pathfinder r51, diesel in-line engine

[NorwegianPathfinder]

Just got back from a manditory checkup and was noted that there is a fault with the turbo charger.

The mechanic said it is either the charger that is worn, or it's a leakage somewhere in the system itself.
There is a distinct whistling sound coming from the turbo when the engine is speed up. Could sound like the turbo is working overload or is worn out.

The easiest thing would be to simply change the turbo charger, which is affordable, but it would be a pain if that didn't solve the problem.

Any idea as to what is more likely of the aforementioned faults?
And any suggestions how to find out the fault?