Is it a breach of contract when GC employee's do part of my (subcontractor) work?

Who installed the line that is leaking? If the GC did (and you did nothing to damage it) then the leak is his issue (or whichever trade damaged...

Bought a new insurance policy

If the accident happened before you bought the policy (before the policy was bound) and you now know about it, you have to withdraw the claim-to do...

Most states' contractor licensing laws require that a icensed contractor have a written contract and without one, he cannot enforce a payment...