@Razer11 - you need to add slot for that decoration. Try to copy that slot from other car that have it.
If car don't have any spoiler slot, add it from different car too
I know it's SLRR part of forum, bud I don't want to make new tread for this:
What can cause Forza Studio to crash on startup? It have been working before, but today, when I try to run it, I got instant crash. I've tried with reinstalling XNA Framework 3.1. I'm on 8.1, so I cannot reinstall .Net Framework 3.5 (many tutorials on web say to reinstall it).