normals, faces, arghhhhh

Hi., This model, and many others that i have, have problems, i believe in the normals, because they give weird lightning in game. I already tried selecting all the faces, and welding\unwelding , and while it becames ok, and i save it, when i open the model again, the problem is back. Is there a fix to this ? Or the model has to be done all over again ? thanks, Bruno