I soaked the swivel in hot water for a few minutes and it really seemed to work, the swivel is spinning as never before!!!
I have to try some loops again and see how it goes. I thought of applying some sort of lub but was afraid of making it worse.
If this is the solution of our problem we just have to soak it in hot water every time before a session.
Just like a woman ... requires lots of attention and care.

Thanks again for all your comments.