Hey there Natureboy,
It sounds like the up and down position stop pins in the armrest shaft have either broken off or have fallen out.
There is a way to pull the armrest shaft out of the seat, it is a little tricky, but rather easy overall. If I recall correctly, this is how to remove an armrest for this particular vehicle.
With the armrest in the down position (facing towards the front of the vehicle), rotate it upward into the upright position. Push inward at the base of the armrest by the shaft as you rotate the armrest into the upright position and then into a backwards position. As you rotate the armrest into the backwards position, there is a release slot that allows that armrest shaft to come right out.
I believe that those stop pins can be replaced, if not repaired. Although, I do not know where to advise you to look for armrest pin repair kits.
Hope this helps.