Could/should the seller have disclosed this to me!?

[Jonathan Chique]

Hello all, I’m new to world of real estate investing and just closed on my first multi family property in October of last year. 
I recently discovered a leak in the basement coming from my 1st floor toilet. It seems like the previous owners or manager used a piece of metal to cover up that leak since the metal was rotting of water. After a plumber repaired the leak, he told me that the plumbing System did not have ventilation. He would have to break through the wall and add a ventilation system. Which would cost over 5k. None of this was disclosed to me or mentioned in the inspection report. Is this simply a done deal, nothing I can at this point or is it worth bringing up to mine or seller’s attorney? Any advise would be appreciated, thanks.