I see you trying to change the TIM and see if anything changes. Given that your laptop is way outside of it's warranty period, any replacement parts will be from third party vendors which in essence means that they aren't the best of quality which is why you may give benefit of doubt towards the fans being faulty 3 times in a row(or that the batch that arrived was faulty in itself) and since the laptop itself is outdated, shelling out anymore expenses on it is a waste of resources. I'd say that it's run it's course and a new laptop would be worth your investment+ears.