Eveofchaos
Instead of handing over the spot for another persone to have that thunder guy's legacy, he should first make a oath with that person before even saying anything about its content to hand between a third or half of resources plus the previledge to see all the data, techniques, spells and any type of knowledge he will get from the legacy before giving him or her (most likely) the chance to have it while making absolutely sure to emphazise the terms about not revealing the oath at all no matter what!