I’m not going to be able to provide you an answer - but having missed your previous discussions and only seeing a couple of your posts, how do you know your car has a bad headgasket? You describe losing a gallon of coolant every 6-7 weeks, which seems like a lot to not have any in the oil or to notice more coming out the exhaust. Are you sure you don’t have a cracked coolant tank? They were pretty common on these cars, and easy to fix.