Transfer box oil leak

[S3DAVE]

Hi Had MOT today which passed with flying colours!!
I noticed though there was a small amount of oil on the rear of the transfer box where rear diff comes out. Its not a lot and the guy said not to worry. What do people think???
Also what oil is in the box? Gear oil or is it fed from engine?!? It didn't smell like gear oil?! Anyone else had this or rectified this??................

[S3DAVE]

Not been anymore appear since i wiped it. Could it be some spilt from service and drained down back of engine!? My drive is steep and I always reverse on.