Just a note since there's often a lot of confusion about what pivots on what. The arms have a bushing in them that gets clamped in place on the mounting stud. The arms themselves then pivot on that bushing and not on the stud. Greasing the stud will not make the arms move more easily. It just avoids the stud getting rusty.

If some WD40 and followup oil does not restore the arm motion to smoothness you may need to take the bushings out and clean all the works. On the front of the arm there is a washer that will have a step or teeth on it that sits on the front of the bushing so when you tighten the mount screw it doesn't jam the arm. You need to gently and evenly pry off that washer. Once you do you can push the bushing and spring baseplate assembly out the rear. Take careful note of how the spring base area on the back side of the bushing goes together as some of them are pretty funky and you can lose out a lot of hair scratching your head trying to figure it out.

Some pivot bushings are plated steel. If the plating wears away and the steel rusts you will find that you need to get agressive with some medium or fine sandpaper to polish them up. Others are proper brass or brass and stainless. But the old grease can get pretty grungy from dirt and drying out as well. Some scrubbing and a light smear of new grease and you're good for a lot more years.