repaired 2011 Kia Forte

I am trying to determine the best option available to me, after getting my vehicle back from Safeco's preferred body shop, with a severe transmission fluid leak. The transmission did not leak at all prior to the accident. Safeco claims the transmission had to be damaged prior to the accident. Since the car could not be driven, and I had to have transportation, I paid $2260.00 out of pocket to have the transmission replaced. The insurance company has taken the position that since the transmission didn't take a direct hit, the busted transmission casing had to have been previously broken. The advantage of my using their preferred shop was that any damage that was missed, or found after the initial inspection would be covered. At least that is what Safeco, and the shop both told me. Where do you recommend I go from here?