The only obligation of the insurance company is to pay for those damages which their insured would be legally liable to pay for as a result of damages he caused. If there is a question as to whether he did cause the damage then it is up to you to get the information needed to show that it was in fact damages that he caused. There is no way of knowing if the transmission problem was caused by the collision or if it was going to be a problem regardless, however, if the inspecting mechanic states that it was cause by the collision then the company will most likely pay for the damages as well as for the inspection.