Hello C'est si bon,
In my pre-AMEL days, I had a boat on which the swivel stuck. Some one from Hood sails told me to do this: run water through the swivel, then soak it with WD-40. Then wash again and soak again and wash again . This worked . I know that WD-40 is not a lubricant but it is a strong detergent and removed all the accumulated dirt. It makes a mess on the deck, but washes off with lots of water.
I now do this about once a year and it has worked for 19 years.
Ladybug. S/M 216. At anchor in a sheltered bay north of Newport, RI