Do I need a lawyer?

About 2 months ago husband and I purchased a brand new car. When we were driving to our vacation the engine became very loud and it was difficult to accelerate. We made it to our house and called roadside assistance the next day. They towed our car to the nearest dealership. The mechanic there told us that our catalytic converter was missing, but had been replaced with an aftermarket part. This part was improperly welded and incorrectly installed. As we drove the improper welding wore down and more and more exhaust was leaking into the car. We were unknowingly driving a dangerous car. In the short time sincw we bought the car we had never had it to a garage or a mechanic, so the only logical conclusion is that the aftermarket part was installed before we purchased the car. Which means we paid for a brand new car, but did not receive a brand new car. I feel that the dealership should give me what I paid for, a new car, and reimburse me $300 that I paid to make the car safe to drive agai