Can I sue my insurance company and repair shop for non-payment of additional damages?

Question Details: My husband had a wreck going 25 miles an hour in which he rear ended a car, his SUV died and caused him to roll downhill into the back of a second vehicle the brakes would not work since the SUV had died. The insurance company referred to him to a body shop for estimates and repairs. The body shop took pictures of the outside of the car, the grill, the bumper, etc. The guy opened the hood and looked in but did not take any pictures that we are aware of. The body shop sent the estimate and told the insurance company who agreed to pay the claim. The repairs were made. Then, 3 months later, my husband was driving to the airport before dawn and hit some debris in the road. When he got to the airport, he realized that his gas tank was leaking so he tried to make it to the dealer but ended up having to be towed. When the dealership looked at the vehicle, they told him the gas tank was punctured but that they were looking at the length of the underside of the SUV to make sure there was no other damage and found the radiator was filled with oil. This led them to search further and they also found a blown head gasket and oil all in the system and told him that his radiator and engine would need to be replaced. They told him that the radiator and head gasket damage had occurred a while back and had it been caught when it happened, it would not have resulted in an engine replacement. The insurance company has denied the claim saying the radiator and head gasket damage was not a result of the wreck and that they are not liable for normal wear and tear on the vehicle. He has the vehicle serviced regularly and at the last oil change there was no damage and no leaking head gasket. They also check the fluid levels during oil changes so they would have known if there was oil in the radiator at that time. He keeps the receipts so we have a record of the maintenance. We are sure that the damage to the radiator and head gasket was from the impact of the first wreck. What recourse do we have? Would we have a case to sue the insurance company and the body shop for repairs of over $5,917 includes tax for the repair of head gasket, radiator and engine plus the $500. deductible of initial repairs from the wreck since the repairs were not found/made by the body shop chosen by our insurance company?

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