I took a quick look at the EBAY ad. Here is the most helpfut part for you
so, the good news, imo, is that since this was his car and he was the original owner, he should not be able to deny knowledge of the accident with any credibility.

the bad news, imo, is that you d/n have his statement in writing, which would have made a very strong case. The other big problem, imo, is that you had your Dad check it out before your purchase. In order to determine damages, imo, you would need to find out what the true mkt value of the vehicle is v. what you paid for it.

It might be in your best interests (limit legal fees and your time) to see what, if anything, the seller may be willing to refund you. In any event, please let us know what happens.
good luck.