This should work like this:
Create Mechanic class - Mechanic can repair track, egnine, commander turret, cannon - dont be afraid - ACE team have done this - just ask them how
Equipp every vehicle with tools kit.
Enemy sighted* - turn into combat mode* - allowcrewinimmobile
After engaging* - no enemies in sight* - turn into aware mode* - disembark ONE mechanic (driver if alive) to repair the track.
There is no way to make this more relistic. I will not edit every downloaded mission wasting time to eneter "allowcrewinimmobile", this shoul be done automaticly.
Please make it possible fast, its gamebreaking feature, specially in modded content (RHS) where most of time track being damaged by RPG fire, my whole crew dies beacuse such stupid incident.
* - ITS ALREADY APPLIED, just modify it a bit.