One of the things you want to do is to install a grease fitting so that you can grease the clutch arm from time to time. With that in mind, I would get a fitting and a drill bit for it.
Drill the arm in the middle being careful to feel for the break through from the aluminum arm to the steel shaft it rides on. Then you can use the hole to inject penetrant into the arm. By applying the penetrant from the ends and the middle and a lot of movement on the arm, you should be able to free things up enough to get the shaft out.
Once you have everything apart, you can clean up any dings the bit did to the shaft and install the grease fitting.
One thing, when you drill the hole, make sure the arm is in the normal position it would be in when the cable is attached and properly adjusted. This will make sure that it will be easy to get your grease gun on the fitting.