Do you mean the center line swivel? That sucks. I suspect those are supposed to be sealed bearings, maybe you had a faulty part.
I've been using them for a few years now, and while not perfect, nothing has seized up on me. But then again, I rinse my bars with fresh water after most sessions. I also spray that center line swivel with a dri lube (like
McLube) on occasion.
If there is a way to self service that, it'd be great.
If not, you can buy a new one but they are pricey (
here). Call up Slingshot. If you bought it within a year they may give you a free warranty replacement on that part or a better price. I've always found them very responsive when I call with a question.
The bearings used to rust for some people on the old CL setup, and they sold the bearings
here. But that's a different part. Salt water is going to rust stainless steel also if left on it for a long time. It takes a much longer time than regular steel, but it eventually happens.
Good luck and let us know what you find out.