One more...I don't really understand the reason they used the square headed pin. I guess its so the pin doesn't rotate and wear into the outer bracket holes.
That’s my understanding as well for the square headed bolt.
My car sat for almost 40 years - the pin is seized in the pivot. I soaked my parts for a month to no avail.
I even got it hot and used a press, so soap.
Last trick I heard is to get it red hot then hit the pin/lever with candle wax. Sort of works like soldering plumbing, the wax gets sucked in.
If that doesn’t work then I am going to use a vertical mill to drill out the square headed bolt.
