thats no good about your trusty Jack , I too Love my tools and take great care of them as well , and have come to the concusion you carnt lend tools they never come back the same .
I have seen a disc rotor Cut off by the pads

, the guy came in with a rattle in the front

, not that the brakes were pulling due to disc not conected to hub anymore

,
your friend needs a wake up call

, he takes care of your tools the same way he takes care of his life , by the sound of things , make sure he pays you and doesnt use your tools anymore , thats the only way he'll learn