I would expect that type of tape to have a rubber washer on the inside.
shut of the water to the line and use a wrench to take the tap apart, if it is a rubber washer there should be replacements for it. A new rubber washer would be soft and make shutting of the tap easy
What the inside of the tap should look like not the same tap but should be close.
https://www.google.ca/search?q=repla...de8o4WzP14M%3A