Moving out of Zaire and Namibia is not clear to me.
The rule says that you can exit Zaire or Namibia only by the road link.
Does it mean that one cannot exit Namibia or Zaire to the other adjacent 2/3 adjacent regions ?
Both Zaire and South West Africa are both oddities in the rules and are dealt with differently from each other.
On moving out of Zaire, you can leave Zaire using road movement but do not have to. Rule 14.1.1 allows movement into any of the 4 adjacent regions. These adjacent regions are classed as 'clear' terrain (presumably only for movement purposes)which means you can continue moving up to 2 further regions as long as those 2 regions actually are clear terrain.
South West Africa works differently. You can only move out of South West Africa using road movement via Peira de Eca (see 14.2). You cannot move from South West Africa into either of the 2 clear regions on either side of Pereira de Eca.
You can move into both Zaire and South West Africa from any of the adjacent regions. You can also exert retreat zones and support in combat any of the regions adjacent to Zaire and South West Africa.