There were at least 2 different designs, but both are similar
If memory serves me, the arm slides back and forth in a metal channel with a rubber buffer that the arm goes up against to absorb shock.
At the very outside end there is a tab bent over that has to be straightened in order to slide the arm out the back.
The other design has a pin rivet type of thing at one end and a clevis at the other. You'll probably have to drill out the riveted pin.