Can you post a pic of the other side of the armrests? These are rather simple affairs with the shaft mounting on the seat, the armrest slipping over the shaft and then the nut or circlip being used to secure the armrest to the shaft.

Then a plastic cap is popped over the hole on the outside so it looks nice and tidy. Some of these, most in fact, have some small vents in them; some do not.

Pictures of everything you have in this area would be helpful.