This anonymised case concerns a BMW xDrive examined at BEM-TEC. The illustration does not show that customer's car.
The symptom was most noticeable at low speed
The car juddered at walking pace and while turning. The basics come first: tyre size and wear, all-wheel-drive fault codes, and transfer case servicing and adaptation data.
When oil and calibration do not change the symptom
In this case, transfer case oil and adaptations had already been addressed. Another calibration did not resolve the symptom. After basic causes are excluded, unchanged symptoms can point towards mechanical wear in the transfer case.
Repair decisions follow the findings
An xDrive symptom should not lead straight to expensive parts replacement. First check tyres, other possible drivetrain faults and how the symptom varies. Only then can transfer case repair or replacement be justified.