Look at this on a smaller scale. Say I purchased a prepackage item from the grocery store. Only later, once at home, do find that the package had hidden damage causing the product to be bad or not good quality. Should I not expect the store to make it right? The store will give me a refund then ask their vendor to make it right to them.
How is a truck any different? If the damage was hidden, and has not been corrected to OEM specs, then the dealer should be responsible. Then, after the dealer makes it right to their customer, the dealer should seek restitution from the party that traded it in without full disclosure.
If it was just a small fender bender and it was repaired, I don't see this as being a big deal. However, if the accident was bad enough to have "Branded" the title, I would ask the dealer to purchase the vehicle back from me for what I paid less an agreed upon amount per mile that I used the truck.
I would take the truck to an unbiased shop and get them to look at it. I would also see if a police report was done for the accident. I'm sure the OP's attorney will do this.