Thanks everyone for the replies. To update, we've decided to go with the siphon system the engineer we've consulted and at least two of the contractors we will contact have suggested. The young, skinny guy who volunteered to crawl into the lateral pipe is relieved he won't have to take photos of the damage to the old system. The engineer convinced us that a sleeve wasn't practical, and replacing the current mechanical system would fail at some point in the future. I've noted that some contractors don't like the siphon. We will fill the old system with concrete and hope the siphon system works the way it should. I appreciate the help with ideas!
