Unless you live in an area where new ones are hard to get and/or expensive, I'd just get a new one. They are only $30-$40 in the U.S. Given that you don't know the history of it, I wouldn't take a chance on it in my car.
That said, I think the coil innards are filled with resin, so it's possible things may be OK even if water has gotten inside. And the crack could probably be easily filled.