Always thought the outside mirrors were seized and would not adjust. Removed the passenger side mirror to replace the cracked mirror. I found that the vertical shaft is six sided and not adjustable once installed, only the horizontal plane is adjustable. Am I missing something?

It has been a while but I am pretty sure my mirrors, the actual mirror portion, is adjustable vertically and horizontally. Additionally, the mirror can be pulled in to be parallel with the side of the car, along the window. Maybe someone modified the mirror you have?

Factory mirrors are adjustable "horizontally" as well as "vertically".

I fold mine in against the body when I put the cover on.
AND I put the antenna under the drivers side mirror....

with the mirror removed, invert, and squirt PB Blaster, let soak a day. next day, the nut should be able to taken off with a socket, disassemble and clean off all the corrosion, there is a coil spring in that shaft area. on reassembly, don't torque too tightly, otherwise you can strain the the mounting base to the point of cracking, then you'll need to source a mirror base. i have never been inside where the glass is mounted, so the only thing I have ever done is sprayed silicone where the mirror pivots.

If you gently remove the seal around the outer edge of the mirror, you can remove the glass. Once it's removed, you will see a nut that controls the tension for the vertical movement. Do the same thing here you did with the base.

Remember, too little tension will cause the mirror to vibrate due to engine and road vibration. Too much and you can't move it up or down.

Like this:

Click to view attachment

Click to view attachment

I'm pretty sure I've got a mirror like offwatch too. The car is stored for the winter now but I'll check next time I'm going to do some work on it.

Lube !

The stainless steel of the big part of the mirror is not real thick and I have seen
several where it is split/torn where it joins the elbow part.

Be careful forcing the mirror by grabbing and twisting !

Finally got the camera out to get some photos, as you can see it is six sided and only locks in on those positions. I thought the piece in the base might be separate but I have soaked it in PB blaster and tapped on it and it feels like it must all be on piece.

I take it back, just tried tapping it again and the center piece did come loose from the base.