to fix broken parts you should play with back to parent tool in Zmodeller move part and then press back to parent them export from porgram and place in rpf file with vehiclemods.
use Zmodeller, open cars in that program. I didnt do that. It was my friend, but he don't want to tell other how to do that. I think some tutorials on youtube will help you.
to fix broken tuning parts you should manually move axels of them to match with car model axle. Thats the solution! My friend already fixed some models using this way.