Modded parts have no skin

I cant figure out why when I mod vehicle parts, the skin doesn't apply to it. I could literally duplicate a fender and give it a new name without changing anything else and if I apply a skin, the fender will be white or base colored while the rest of the vehicle will have the proper skin.

 

every time you edit a part the skin UV map (2nd uv layer in blender) probably is changed/broken
if you have not applied the correct material, the part in question will probably be light grey/missing texture, and if the UV map is broken, it will probably be base colored/may be broken looking

to fix this you need to edit the 2nd layer uv in blender to make it compatible with skins again, sometimes this is harder depending on what types of modifications you made to a part

 

I dont use blender, and Im not great at UVs. So I guess i thought there was an easy fix.