Do black truffles go bad?

My parents were given a black truffle in the p�rigord regon of France 18 months ago from a local farmer who had put it in a sealed gl jar with a bit of brine. However this was 18 months ago - they've kept it in the fridge but will it have gone off?? What's the best way to cook it / use it to flavour olive oil?? any ideas? thanks.