End of flip curve ball

[Steven Denio]

Hi all, looking for a little wisdom. I'm in the middle of a flip due to be done with construction in a little over a week. Just had a some pitting checked out that I found in the steel galvanized water piping under the house. The plumber recommends a full replacement of all the Plumbing underneath the house. I am already way over budget and the bid number could eat all if not most of my profit at this point. Should I, A) just put a patch on the leaking pit and let the next home owner have some work to do in the next few years or, B) do I need to replace the whole under carriage of the homes plumbing? I don't like cutting corners and want to deliver a solid home as we all do but it is an old home, my inspector missed the pit and the plumber I am currently working with initially missed the pit too, when I pointed it out he found out that the whole plumbing system was toward the end of its life. 

Has anyone had experience here? My initial thought is to fix the pit with a patch and wrap the plumbing in foam insulation, is there anything unethical about that? The plumbing could still make it years for all I know. 

Thanks in advance for any replies.