vehicle addon damage problem, spawning new car

[microbee]

Hi guys, first post, I've been wading through the zmodeler learning curve modding GTA5 vehicles.
I'm half way through the trial.

So far so good, learning as I go with a few hiccups on the way.

I'm having a problem with collisions when a part such as a bonnet flys off the vehicle a whole car spawns instead of just a bonnet or bumper.

Thanks.