Currently, the only ways to replay a system from a finished job are to save the URL or go back through the screen for that particular job. I think once a job is finished, the cluster it's connected to should be shown on the clusters screen, possibly in a "finished jobs" section (like how public clusters and your own clusters are separated).
We'll definitely consider this. We need to do a user experience pass on the clusters page anyway. It currently works differently than the other lists, and I agree that having to go through finished jobs is a bit weird.