Some random thoughts.
If the system was leaking badly the po may have run it out of oil and ruined the pump.
Just as you can not see the electron flow in an electrical circuit without a meter, the only way to know the condition of the pump is to hook up a guage on the pressure side. It should read around 700 psi.
In addition to a worn or damaged pump a plugged filter can cause a low flow situation and weak steering.
They are self bleeding. If the pump is working properly just using the tractor, driving it around, etc will purge any air out of the system.
A non (or slow) responsive steering system can be caused by a broken plunger spring or springs and or crud in the hydraulic block in the column.
If you go into it far enough to replace that upper seal I would surely pull the hyd block and clean and inspect it. I would also replace the lower seal or you'll wish you had someday when it begins to leak and you have to go back in there.
There is a speedi sleeve available for the upper seal surface if yours is rusted, pitted or grooved.
I have never heard of pullung your self up by the wheel damaging the upper seal and have been doing it that way on my 3000 for 15 years with no issues. There is a rubber and brass bushing in the very top of the column that should prevent any bending of flexing of the shaft enough to damage that upper seal.
Lastly, if it were me I would pull the steering box completely off the tractor and go through the bottom end too. That oil has only been in there for 50 years and it could probably use some new stuff, a pair of sector shaft seals and an adjustment in the bottom.
My two cents...
