I'm in the process of removing my sidewindows from my 52 3/4 chev pu.

I have everything disconnected except for the wing window post that goes down into the door. There seems to be a standard slotted screw holding the post in place. Is this correct? I tried turning it with a big screw driver and it won't budge. I can't see what is there, but I can feel it. I don't feel a nut on the other side. It must be a permanent type of nut.

Any suggestions on how to get this off? I didn't try too hard as I didn't want to strip the screw.

Thanks for any help
Mike