1. Find your usual PC mechanic, who can only repair parts to a 'barely damaged' state, at best;
2. Find a master PC mechanic, which are very few and far between;
3. Entrust your ride to an NPC mechanic, who will be able to fully fix it; or
4. Buy an entirely new part, which in the case of engines or transmission can be very expensive.
I think vehicle mechanics, for the sake of RP and player economy, should be reversed: light damage should be the easiest to repair, while horribly damaged parts need a master to salvage. This would stimulate the PC economy, allowing junior mechanics to take care of the small stuff while the pros are brought in for heavy damage. This would make it a lot easier to fix vehicles and thus damaging them would be more conducive to generating RP and profits for certain people.
Also, please change the failure message for component repair to something more generic. As funny as it is to imagine the phrase "There's nothing more I can do for this" being a mandatory part of mechanics training, I would prefer words not be pushed into my character's mouth.