There's no need to remove the turbo or change any parts based on a guess when you can establish the VNT operation within a few minutes using cheap tools.
On a Euro 3 D5, if you follow
my video here, you can diagnose or eliminate a faulty actuator and you can physically see the VNT arm moving which in turn is moving the VNT mechanism through its full range of travel.
If the actuator holds vacuum and the VNT arm moves freely through its full (10-20mm) range of travel, the problem is elsewhere.