A major line is down. You and Bob, the only maintenance electricians available, trace the problem back to an 800A breaker. Your distributor doesn’t have a replacement for that breaker in stock and it will take 10 days to get it. They do have the rebuild kit in stock however, and it costs a fraction of what a replacement breaker costs.
The plant engineer says this is a no brainer, order the kit delivered and rebuild the breaker. You’ve never been trained in how to rebuild