Transfer Shift Actuator

[Tom 1981...]

Hi all, 

I own a Navara Dci Tekna 4x4 Shr DCB (2017) and have had an intermittent 4WD warning fault for a little while. My mechanic says I need a;

Transfer shift actuator

But usually this part is only sold as part of the whole transfer box which costs about £4000. Has anyone else had a similar experience and is there a way to find out the part number for the Transfer shift actuator and purchase it on it's own? 

TIA

Tom