editing a modded cars textures

[lynxyboi]

hey guys, i need some help. I have a 300zx z32 mod, i have changed the wheels etc.. but the down side of the car is a dirty windscreen, and yes I know about content manager and the fix. I have applied that and it has fixed other cars but I'm still struggling to fix it. I use vr, if I stand up and look from out side the car through the front window its perfectly clear but from the inside looking out its dirty and I cant seem to find how to fix this. its like the creator put the texture on backwards, I'm guessing so the driver can see but outside the car it looks dirty. I tried removing the windscreen through 3dsimEd3 and exporting through KS editor and it wouldn't let me like it did with the wheels. in direct sunlight its worse, cheers