If the crack veers off toward the periphery of the spigot then it's probably time to change it. If it's more or less vertical, then it probably could remain servicable by drilling a hole through the spigot at the end of the crack to relieve the stress.
30mm, so that'd leave you about 25mm if you got it machined off upto the crack? I have a TS1 barrel that's machined down cos of a cracked spigot. the quatrini's don't have a spigot, so I'd have thought if you have 25mm of spigot then even for locating purposes its doin its job