Get a couple of quotes to get a decent (to a standard you would be happy with - not a back street garage) repair done and tell the little punk to cough up...........if he can't cough up then go then 'invite' him to let his parents he needs bailing out of the shit!!!

If they won't bail him out then remind the little bastard that if you report him to the police he'll get points for driving with no licence AND being uninsured and he'll have that lovely little provisional licence (or maybe full one if he passes) of his revoked and it'll be 5 years before he'll be able to insure a little shitbox car again (insurance companies come down VERY hard on people previously convicted for no insurance and he'll have to declare them for the full 5 years) so it's REALLY in his best interest to not get the police and insurance involved.

So the choice is his........he sorts it, his parents sort it, or you let the police sort it and he gets right royally fucked over!!! Either way you are owed a proper and full repair on your car!