I bet someone's already figured this out, but I figured I'd post in case a couple of you might not have... I've got a '93 F-150, actually pretty good shape overall although both bumpers need attention. But inside, those crappy vent assemblies made it look very ghetto, because of course like all Fords "of a certain age" all the vanes in any given assembly point every which way. Well I figured I'd see if I could fix them myself rather than pay the $25 apiece for new ones from LMC. turns out all of the vanes were busted in the same place - a little molded plastic pin that fits into a sliding piece to keep all the vanes pointed in the same direction. You can remove the vanes simply by bending them slightly in the middle. So I pulled 'em all out, used an unbusted one as a template, and inserted a piece of wire in the busted ones. I just drilled a hole in the end where the little plastic nib was broken off - I think I used a #52 or #51 drill bit, I forget, and a pin vise - and inserted a piece of 14AWG copper wire. Then I snipped the piece of copper off just a little longer than it needed to be and finished with a flat bastard file. Reassembled et voila, un-ghettofied vent assemblies, all for the cost of some scrap wire that I was going to throw out anyway.
I'd keep them lubed up well with silicone or other non-greasy lube, because I can't remember the last time I saw a truck that didn't have at least one broken vane...
nate