VK,
I should have mentioned this in my first post.
Another item that is a common coolant system problem is the plastic coolant fill tank in the rear trunk.
They develop hairline cracks with age.
You should remove the carpet and the sub floor in the trunk.
Strip everything out Down to bare metal.
Then when you pressurize the coolant system you can check the plastic coolant tank as well.
Keep me posted..... if you need to replace the coolant tank I can give you a few pointers.