Plumbing Inspection Question

[Joseph Schommer]

Hi Bigger Pockets Community!

So, I'm under contract on my second SFH and I got the sewer lines scoped (like a good BP member). They found something! There's a belly in the cast iron sewage line that's about 10' long and about 40' from the house causing the sewage to settle and "back fall" a bit. They also found a lip on the pipe that shouldn't be there. I watched the video so there's no foul play here. The seller (a real estate agent) has never had any problems reported, and thus won't pay for any "preventative maintenance".

The estimated repair is $10,500. SO, This is a major Cap Ex!  The property cash-flows $170 after Maintenance and cap-ex reserves are taken out, so this repair kills my cash on cash for 5 years...

What do you think folks?  IS it something that I can ignore for a while?  Why would a cast-iron pipe have sagged so much (assuming they put it in right)?  Murphy's law too right? 

I super welcome all your feedback and love what BP does .  Thanks in advance.