Should I let the contractor come back and try to fix the problem himself?

In many situations, yes, and depending on your specific contract terms, you may actually be required to allow this before you're legally permitted to sue. California's Right to Repair Act itself generally imposes a mandatory pre-litigation process requiring you to provide the builder with written notice of the defect and a genuine opportunity to inspect and attempt repair before you can proceed to file a lawsuit.

If you do receive what appears to be a genuine, good-faith repair offer and choose to turn it down, it's important to document specifically why you're rejecting it, whether that's because the offered repair doesn't address the actual root cause, uses inadequate materials, or comes with no warranty on the repair itself. Refusing a legitimate repair offer without a documented, defensible reason can weaken your damages case later, since courts and the pre-litigation process generally expect good-faith engagement from both sides of this exchange.