what I meant is that they just draw half of the element, since it's splitted in two halfs in the original model, so if you want to fix it modifying the texture, you'll have to copy the detail, flip it and place it side by side with the other half, to have a complete element.
The other way is to fix it modifying the model, by adding as you said an edge.
The first way will require to change how the texture space is used, I suppose.
The best way just depend by how many polys are we talking about, so how much the pcount will be increased, and if the texture space usage has to be changed anyway.
I'm sure about the area between the head and the middle section, but I don't remember if there are other areas too.