I also would have expected a soft metallic gasket/seal on both sides but it doesn't appear that is the case when I look at some of the original fittings that I don't think have ever been broken on my car. However it sounds as though when others on the forum have broken and reassembled these types of fittings, they have placed such a seal on both sides? The coolant bypass tube on the head is a good example.
Thanks,
Harry