The crack doesn't concern me as much as the possibility that there will be a bunch of hard spots from overheating of the clutch contact surface If you decide you must use that one, drill a 1/16" hole all the way through the flywheel at the end of the crack to keep it from spreading any further. Have a machine shop grind the friction surface smooth, and discard the flywheel if hardened areas show up. A hard spot is football-shaped, and what you're seeing on the surface is just the tip of the iceberg.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!