Had the same problem on my XR2 when we moved the battery to the other side. We forgot the mass connector to the starter motor. The cold engine works fine as a mass connector, but when it gets hot, its electrical resistance rises. With a warm engine the starter refused to do his work, but when the car was pushed, the engine started without any problems. Made a NEW mass connector and everything was fine again. Although it sure is a good idea to take care of the heat problems a turbo makes...