So finally my coolant tank cracked. Good thing i noticed the coolant slowly started disappearing, i was planning to move to G12 coolant anyway , so i was basically somehow ready for this. Got a spare tank last year altho its not OEM, but i hope it will last a few years. In short i replaced the tank with the new one. THe new one seems to be thinner, so i dont expect it to last 20 years for sure, but overall it works.....for now. Flushed the system as much as possible by running the car while the radiator drain plug was open and i was pouring water through the cap on the thermostat housing did that for a while until no foam was forming anymore , when filled to the cap. Then i added twice G12 coolant almost 5 liters first time then ran the car for a while, so it can mix with the water then removed around 4+ liters form the drain and then added 4+ liters of new coolant , hopefully this ended somewhere in the 65/35 coolant/water. Next time i am replacing all the other pipes. I have already purchased an aluminum housing from Jaguar and i am planning to fabricate the lower and upper plastic pipes part from aluminum. I saw the chinese have manufactured the plastic part that mounts to the heads, so that one i will probably not fabricate as it look expensive to be done from aluminum. My question is about thermostat. Is it removable part from the stock housing or is it part of it. My car is Gen 1.