The border crossing at Sendellingsdrif, dont go there unless you get your carnet stamped before you arrive as there is no customs office there, I had read blogs on wild dogz adventure site but obviously South African bikes get through without carnets. If you do wish to try it you might be able to get it stamped at Alexanderbaai border crossing 70 k's away but you cant actually cross at Alexandabaai as its into the daimond mine area and you need a permit. Let me tell you great riding around there.
This is a later updaqte sorry for that if your reading
I actually found out later you dont need to get your carnet stamped out of South Africa when you enter Namibia so I could of crossed at Sendellingsdrif you get your carnet stamped in when you come to south africa and then Namibia Botswana Swaziland and Lesotho are all part of the same union so you dont need to get the stamp out till you go to Zambia or Mozambique sorry I didnt update this earlier