Slick 60's

The rear channel in each door is broken at the top mounting point. Any felt or rubber or whatever would have originally been installed has disintegrated. Do they just tend to break there simply due to age or is it because whatever would have been in the channel is not there, which allows the window to move more than it should, applying excess force and vibration to the channel and eventually causing it to break?

This is the driver's side. The passenger's side is broken right at that bend.

The picture you show has the nut missing for installation. Most likely broke when someone tried removing the screw that holds the part in place. As to the window channel, that would need replacing with new for about 35$ each plus shipping costs. I suggest Dennis Carpenter and just buy the whole door kits with new front channels etc. at 200$ as set. As to the rear pieces that are broke, the nut slides in the little square slot, and can be found on any Ford truck with the same cab design. Again It may take some patience to get the channel out without destroying the pieces. Takes patience and no force, PB Blaster soak and let set then soak again. Once you get the screw to move some then liberal spraying with blaster and work back and forth, until screw comes out. If, the bracket breaks, save the parts get the screw out of nut and weld the parts back together. Or fab to your idea of right. Just remember you have to be able to adjust the slide once it's been put back in.

More than the nut is missing. Part of the sheet metal bracket itself is gone. The screw is just plain missing so I don't know the history there. Didn't find the nut or remainder of the bracket in the door.

I haven't removed the passenger side yet but all screws are present and the bracket is simply cracked.

Fixed them, hopefully well enough to get at least another few years out of them.