Doesn't really matter if the car was wrecked or not. ALWAYS check to see if both the block and head are flat, especially if the head came from another car. Simply taking a head off a car is enough to warp it, especially if you're clueless about the order in which you take the head bolts out. No surprise to me you're leaking coolant into a cylinder, if you ask me. Have you been re-using the same head gasket?