How to fix missing parts on vehicles
Missing parts on your vehicles are caused by either the streamed files needed for the modkits not being present or two vehicles sharing the same modkit ID. A modkit ID is very similar to a carcol ID. It's a unique number (three digits and greater than 300) that is assigned to a modkit (a part of a vehicle). Sometimes, by pure happenstance, two vehicles have the same modkit ID, which causes both vehicles to not properly show this part. Fixing it is relatively simple:
<kitName>{SOME NUMBER}_{MODEL NAME}_modkit</kitName>
<id value="{SOME NUMBER}" />
<Item>{SOME NUMBER}_{MODEL NAME}_modkit</Item>