Your auto insurance company would not cover this pre-existing damage however you may have options regarding returning the vehicle depending upon the laws of your state.

You can check with your state's consumer protection agency to see what your state's lemon laws are regarding this type of situation. For example in Missouri there is the MO New Vehicles Warranty Law, commonly called the "Lemon Law," which protects buyers of new vehicles by enforcing the manufacturer's express warranty. The MO Lemon Law does not apply to used cars.

In MO New-vehicle owners must report problems or defects in writing to the manufacturer to use the provisions of the Lemon Law. The manufacturer must be permitted a "reasonable" number of attempts to correct the problem.

Normally state lemon laws only cover new cars though so if this was a used car likely any type of lemon law would not apply to your vehicle. If your car was purchased with a warranty insurance policy then you may be able to put a claim through this policy.

One notable exception is Massachusetts which has what is called the Lemon Aid Law. It does apply to used car sales. In part this law requires a private party who sells a consumer a used vehicle must tell the buyer about any known use or safety defects. If the buyer discovers a defect which impairs the safety or substantially impairs the use of the vehicle, and can prove the seller knew about it, then the buyer can return the vehicle within 30 days of purchase. Private parties are bound by this law, regardless of the age or selling price of the vehicle.

The Massachusetts Lemon Aid Law allows you to void or cancel a motor vehicle contract or sale if your vehicle fails to pass inspection within seven days from the date of sale AND if the estimated costs of repairs of emissions or safety related defects exceed 10% of the purchase price.

In most states though if you bought the car used and in "as is" condition then normally you do not have any recourse against either the person you bought the car through or your insurance company. Since your vehicle appears to have pre-existing structural damage then you should check into what type of title it has, to make sure that it is not a salvage or rebuilt title meaning that the structural damage was likely the reason an insurer decided it was a total loss after an accident.

If this car does have a salvage or rebuilt title and you were not informed then you should contact your state's consumer advocate, usually can be found by contacting your state's attorney general's office.

You should also check to see if the car you purchased had any type of warranty on it. Warranties can normally be purchased at dealerships, financial institutes or online. Whether it would cover the damage your mechanic found would be up to the terms of the warranty.

If the car you bought from the dealer is used remember that it is important to get a mechanic to check out the vehicle before you purchase it so that any mechanical or structural damage will be known by you before you buy it and take it home.

If the car was sold "as is" without warranty then it is unlikely there is any recourse for the issues you encountered after you purchased the used vehicle. Unless the contract that you signed when you bought the car had a clause stating that the contract could be rescinded for reasons such as the structural issues you found, likely you will be stuck with the car that you bought and the cost of the repairs to correct the issues.

To find out if your state's laws would allow you to take action against the dealer who sold you the car and/or get your money returned to you if there is extensive structural damage that the dealer did not disclose to you when you purchased the car check with your state's attorney general's and office of consumer affairs.