Certain Faces not Appearing after .OBJ Model Export So here's a pistol that I've been working on for quite some time now using Blender 2.79b. It is the first model I've ever worked on and it has been shaping up surprisingly well. The problem that has recently popped up though is the fact that when I try to export the model below as an .OBJ file, multiple faces are excluded and end up looking from this:



To this:



A you can see, multiple faces are suddenly gone and some graphical glitches are present. I'm not really sure if the fact that I applied a Boolean Difference Modifier at most of these meshes has something to do with this issue, but anyways I would appreciate it extremely if you could help me resolve this issue :)
They are not gone, they are flipped. GE don't render the backside of faces, unless you specifically tell them to. 
You can tell that's the case, because the part that's missing in Blender has a blueish color. 
Select that part, go into edit mode and hit CRTL + N
if that doesn't change anything, go back into edit mode and press CRTL + F and choose Flip Normals