To the OP
This isn’t really to help you diagnose and fix your car as there are plenty of people here better qualified than me to do that. I am giving you recommendations should you discover that there was some type of action (deliberate or accidental) as a contributing or causal factor in your situation. Should you pursue a legal solution, some of the advice I have seen here not only could wreck a potential case before you file, it could actually make you liable for damages by the adverse party.
I’m not an attorney and this is not to be considered legal counsel in any way but I am an engineer who specializes in forensic root cause failure analysis on industrial equipment and has to provide expert witness testimony a good deal in warranty and injury situations so I know the process pretty well.
If you don’t decide to pursue a cause of action, just call this good reading and maybe an outline should there ever be a future situation that does require legal action.
Basically after reading your account (and operating under the presumption it is true and accurate) your situation falls into one of three categories.
Existing Condition- the damage was already in progress and the timing was just random. In this case there is no liability to attach to anyone.
Deliberate Action (Malfeasance) – this is clearly actionable in all 50 states IF YOU CAN PROVE IT.
Contributing Action (Nonfeasance) - This is murky because with no intent (lack of mens rea and a questionable actus rea) and assuming they were following an accepted practice or other industry accepted thing that would be considered normal or reasonable under the circumstances then its “possible” there “may” be some form of limited liability depending on a thousand variables and the specific statutes of the authority having jurisdiction. Depending on a number of variables, a party CAN be held liable for a portion of damages even when “innocently” or “accidentally” caused but that’s always determined in litigation and is always costly. It may be shown that the potential benefit is outweighed by the total cost to obtain it thus not worth the effort.
First and foremost- DO NOT talk about this, write a letter (to anyone) or otherwise publicize this situation in any way. Reason being- at this juncture you (based on your OP) do not have a single FACT at your command. Not only could this adversely affect any case you may bring but if you are wrong it can become actionable against you. Sit back and be patient, there will be plenty of time to put pen to paper should the investigation reveal cause and then your words will have more teeth.
Second- you really need a qualified unbiased disinterested third party to diagnose and confirm exactly what the problem is.
Since this party could be called to testify in an expert capacity, they would need to know (and agree) up front to accept this role
Be qualified to stand in that position (a legitimate business, ASE certification or similar, most jurisdictions will accept resumes and work experience in cases at this level)
Have no vested interest or prejudice toward you (or against the adverse party)
Then they need to document (and photograph) every step of the diagnostic process and if applicable list any standard (SAE, Chilton, Haynes, OEM etc.) they use to confirm their process and diagnosis.
Since you probably want the car fixed (regardless of any potential subsequent actions) I would recommend doing the above. At least then you will know what the situation is and be in a position to make an informed and weighted decision should you need to move forward on anything.