Client Claiming I missed a sheetrock crack

I recently got a irate call from a client that was saying that I missed a crack in the kitchen ceiling sheetrock. He went on to say that he would not have bought the house if he would have known and that he wanted me to have all the sheetrock in the the kitchen ceiling replaced.

It had been about a month so I had to pull up the report and also look back over the disclaimers etc. from the real estate transaction to refresh my memory - What I found was that my client not only knew about then crack but had asked the seller to fix it…the seller could not get it fixed in time so they signed an addendum and the buyer received a $500 check at closing to have the crack repaired. Not real sure what to do now. Any suggestions.