I bought a 1988 bmw 735i that overheated soon after I bought it. We did replace the thermostat (it was seized up) and then put a gasket on it. This did not fix the problem and now the coolant leaks out whenever the car is shut off. If the car is running and you put coolant in then it stays and the car will not over heat. I recently read that there was not originally a gasket around the thermostat housing, just a rubber o-ring. Could this be the cause of the coolant pouring out, and if not what could it be?