You shouldn't use a synthetic replacement, since this wire holds the mast up when the sails are off and the rig is loose. Chafe would be a problem.
Ditto. And since the forestay is loose when the jib is up and tensioned, there WILL be chafing of the slack forestay, even if an extra chain plate and shock cord are used.
Good luck with the repairs. Let's see some pics!
Mike
