I'm a professional photographer for 40-years, so I've come out of the world of film cameras ~
Unfortunately, cameras and lenses are extremely delicate and extremely carefully calibrated devices, film or digital.
Reasons why a lens barrel won't move smoothly is that something (a microscopic piece of dirt) is stuck in the threads. It could be that a liquid other than water spilled in, evaporated and left a residue that sized the threads (soda). Just talking a camera to the shore might take in otherwise salty mist that will dry leaving salt in the threads.
Trying to repair camera equipment yourself is a risky enterprise since there are many screws and other parts barely bigger than a grain of sand, and so many variations of screw threads, so they're too easy to lose, and are impossible to replace. There are too many things that can go wrong, and so much specialized equipment to do it right that even professional photographers do not attempt it.
So my wisest answer is to take it to a camera repair business, preferably that caters to professionals, and if the proprietor takes kindly to you, they may do the repair for free. You can also sent the piece to the manufacturer for repair, and it WILL be done right, but may take a while to get it back, and may cost you a bit.
My last recommendation is to go to a reputable camera store that deals in used equipment, and who typically have their own in-house repair or who use a solid repair business.
It could be something so simple and obvious, as I mentioned above, you might get your equipment repaired on the spot and for nothing. It's worth a try.