Tiller Connectors "Frozen" on Tiller Connector

What I'm talking about are the end capss that go on the ends of the tiller connector bar and have the pins that go into the pieces on the ends of the tillers. One end cap is intended to swivel. There's a rivet that goes into a groove that serves as a retainer but still allows it to turn. The other one has a screw that goes into the plastic and so it won't turn. There needs to be some turning allowed so that the steering won't bind. I have just struggled with removing two of these off a club boat. Neither would come close to turning. I lot of Jig-A-Loo and a large screwdriver and a hammer and a vice were required. This boat has only been used in fresh water. Now it's time for me to put it back together and it's really tight. Why are these so tight now? And what should I do to make sure that one end rotates. I've sanded the plastic a bit but it is still very tight.

If it makes a difference this was originally a Classic with tendon tiller connectors updated with the 1957 kit.

Should I go on sanding until it will swivel?