It wasn't from the accident. If it was, the drive shaft would have had to have been pushed forward through the overdrive unit! That was/ is a common problem on the 42/46/47 trannies. The snap ring in the overdrive breaks and ends up in the pan. No big deal, only about 200 bucks worth of parts if the clutches aren't smoked. Sounds like they did a total rebuild for 2500 bucks. I hope you didn't pay that much just to get the overdrive rebuilt!