No ideas on longevity, but do you think it can be repaired with refractory cement or something similar? If you haven't actually looked at it, could it be one of your gaskets is bad?
I've got the original all cast Resolute with the lever actuated horizontal/recirculating burn setup, but I think I am a bit short on draft to make it work properly so I never engage it. I do have a nagging thought about how much less wood I'd have to cut with a newer stove, but have yet to take the plunge on a newer stove with a re-burner or cat for this exact reason. Lots of good information on HomesteadingToday.com or one of the wood burning forums. Good luck! Please let us know what you find out.