It's understandable for a business to try to defend itself, particularly an auto repair place. Two issues: 1) customers must almost literally put their life in the mechanic's hands, and must trust that they don't make mistakes, and 2) complaints like this cost money that many small businesses can ill-afford.
In my view, that's short-sighted. The best thing any business can do is 1) acknowledge the fright, inconvenience, and financial cost to the customer; 2) really look at the issue with an open mind, and research it; 3) correct any mistakes or failure to keep up with the industry - so that customers can continue to trust them.
Some years ago my teenage daughter called almost in hysterics. She had been driving on a busy highway, in a city not known for its lack of violent crime, when her car started making a terrible noise. She pulled onto the shoulder and her wheel literally fell off. Fortunately, AAA responded very fast under the circumstances, and towed her to safety. They found that our local mechanic, a franchisee for a national company, had overtightened the lug nuts when changing her tires and some 3,000 miles later (as I recall) they'd failed as a result. The repairs were expensive. The tire place refused to reimburse my cost because it had been 'some time since they worked on the car, so it couldn't be their fault'.
Like the claimant, I wasn't about to let this go. My kid had been put at risk.
The AAA mechanic had provided my daughter with the destroyed parts and a letter stating that while under-tightened lug nuts will cause the wheel to fall off quickly, over-tightened lug nuts will fail in about the time frame hers did, in exactly the same way. A second mechanic and my internet search confirmed the findings.
Let's just say that I got a check fully refunding my expenses and a letter from the chain's headquarters stating that, while they of course accepted no liability and were reimbursing me merely as a customer courtesy, haha, a bulletin about the lug nut issue would be sent to all franchisees.
We all mess up. Sometimes we have to pay for expensive lessons. I am no mechanic and can't say whether the radiator and subsequently the engine failed because of the clamp, but a mechanic can. If the Kwik Kar mechanic is willing to confirm that, and a second mechanic would also confirm it, this would be a fairly easy case. It's also why a business has (or should have) a business insurance policy, although in some instances it's smarter to pay cash.
If CARS is not willing to review the issue, the testimony, and the photos, and reconsider its response, I'd recommend taking this to Small Claims Court. The claimant doesn't say how much they're seeking, but presumably it's ~$4,000 which should be well within the $10,000 limit. The claimant should be guided by the court as to whether or not they can add a claim for travel expenses to the case.
Is any compromise possible?