Originally posted by Mustaine 
i dont know how you are making it, but for the 190 i made everything was PRISTINE and mint condition on their own layers, and i used over 8 different layers for different types of dirt.
4 layers above that for exhaust.
that may help lining up some of the dirty things, and get that effect you are looking for of dirtying then a virtual clear coat over
just a suggestion 
 I do the same thing I have so many layers i get lost  
ty for tips 
Mustaine