exported .x models hollow looking, 1 sided transparency, need serious help!

Hi my exported models are becoming a thorn in my side, they look ok in blender (I know we’ve all heard this before…) but when I import them to Dark GDK game engine they become partially transparent, (what?) I can see right into my rhinoceros’s ribcage, the uv mapped texture is staring me down from across from where the entrails would be, its pretty disturbing, Ive looked at some forums and read a bunch, so Im breaking down to to you guys about it. Ive tried hitting the z tranparency button, resorting the faces, cntrl-f and once I reset my unwrapped texture and reloded and unwrapped it again and it solved it, but for another model this didnt work out, it still is inside out, I look at the normals and they face out correctly, is this a normals facing the wrong way standard appearance of a model? Or is it improper Z-depth sorting, or is it unwanted ray tracing, or is it an unintentional alpha setting or or… or what? also if you have suggestionsd or a definitive answer I really appreciate it but even better a video tutorial showing how to create this problem and fix it would be supreme, like this is how some people screw up and here is why and the remedy. I am the college library so a multi strategy solution would be best, Unless you know the definitive answer, then a single answer would be fine, that way I can go home and try a bunch of thing if need be, or in the latter case just do the right thing. Thanks so much friends!