Many thanks to Charles and 75RR for all the help!
The head is probably a Siedentopf head, which is better than most heads. The item seen is a linkage which keeps the tube length the same when you change the interpupillary distance. You should be able to access it by removing the three screws that hold the eyepiece on the binocular head. From there you can see where the linkage is suppose to go.
I took out the screws that hold the eyepiece holder in place to get a better look at the linkage. It's a fiddly thing with a lever coming out of the center part of the head and a pin on the end of the lever that engages a hole in a rotating ring on the back of the eyepiece holder. The pin is not fixed and can be pushed in so it no longer engages the hole. I pushed the pin back out and very carefully replaced the eyepiece holder so the pin engages the hole. Now I don't see the lever in the eyepiece. I don't know if it's doing its primary function of keeping the tube length the same because the lever moves so easily I don't see how it can accomplish anything useful--it's almost like the lever isn't connected to anything.
The tube head rod is definitely bent. You can unscrew it and try to straighten it. The round plastic knob also unscrews off. So unscrew the the rod assembly and the plastic knob off and then you can try to straighten the rod like you would a bent nail. If it won't straighten, I may have one on a spare tube head.
I'll try straightening it. To get it out I need to pull it all the way out, and then unscrew it? Will it go back in okay blind like that?
For the stage, the little red arrow you have on your picture is the tensioner for the Y axis and can be tightened or loosened for how you want the Y axis to move. If you have loosened it and it still will not moved, you will need to clean the gears on the control knob. You can just remove the mechanical slide by removing the central holding screw in the middle back with a small spanner wrench. You can remove the whole stage by the quick release lever on the left side and then can remove the top of the stage by loosening the two centering screws and then pushing the stage against the front pin...or you can grasp the front pin and pull it forward and lift the stage out. I would advise you to remove the objective turret, before trying to remove the stage. There is a small knob on the right side of the turret which will need to be loosened and then the objective turret will slide from front to back towards the left corner.
Thanks for the detailed description. I still can't picture how to get at the gears for the motion that's stuck. By "central holding screw" do you mean the one pictured below?
It appears that removing that screw will gain access to the gears that control the direction that works okay. The bottom view below shows the gears I need to get at:
Will these gears be accessible by removing the central holding screw?
As 75RR said, the coarse focus can be adjusted with any suitable rod or allen wrench which will fit in the hole.
I used a small screwdriver in the hole and loosening it all the way doesn't make much difference--the coarse focus is still stiff. I suspect it's due to old grease. I'll probably just leave it that way for now as coarse focus works smoothly, just stiffly, and I don't want to tackle taking apart the focus mechanism.
The phase condenser seems to be missing the lever which controls the flip in/out top lens, which isn't critical because you would leave it in place for all objectives 10X to 100X. For a 6.3X or smaller, it will need to be flip out and you should be able to do it with your fingers.
The lever (both of them) are there. They probably weren't visible in the photo I posted.
Check all the phase annuli by rotating them through all the stops...1, 2, 3 and perhaps D for darkfield, and making sure they are intact. Sometimes the black paint will peel off or there might be other damage. Also make sure the iris works in the brightfield (J) setting by turning the silver ring going around the whole condenser. The left side knob and the front round knob move the annuli rings in the x and y direction to center the condenser annuli with the objective annuli for phase use.
The phase annuli appear to be in perfect condition as is the darkfield stop. I tried darkfield for the first time today and WOW! That really looks cool. It looks like stars on a dark sky. Impressive.