Legal Question in Real Estate Law in California

They can ASK for whatever they want. Whether they are entitled to post-closing repairs turns on whether the problem should have been disclosed. If they can show you knew enough that you should have disclosed the possibility of a water and consequent mold problem, then you may be on the hook for the repairs. Not saying you did this, but I've had a case where the owner had serious water intrusion problems that damaged the walls, so they just put up new drywall and paint and never fixed the mold in the walls or the leaks, and sold the house. By locating the contractor via the permits we were able to prove that the seller told the contractor just to cover it up. That's pretty extreme, but the point is, if you knew enough that a judge or jury will think you should have disclosed something, you have a problem. If you had no clue and can prove it, then it is the buyer's problem.

In my opinion, not your problem. He had two inspections before closing and you already fixed what the buyer wanted before closing. This is assuming you did not know about the mold and neither did anybody else.