If he admitted to breaking it then get him to pay for a new lock and key, as well as a new petrol cap and seat lock with matching keys, the labour costs to install them, and sufficient cash for the hassle and your time taken to get them done. I would also demand the same from his employer is he was doing it on the boss's time. If neither of them cough up then get your local Shyster, Shyster & Shyster firm to go for them and then they can cover the legal fees as well.
If that doesn't work then get the Sopranos.