I finally took a day off from work to tend to the 1948 D24, and to work on a 1928 DA Dodge. On the 1948 D24, I pulled the steering-pitman arm off and let it hang, still connected to the tie rods. I then put a pitman arm on the steering gear from a 1950 Dodge (different design but the splines still fit the '48 shaft). I tried to move, shake, or wiggle the arm attached to the box, but there was no movement - so that tells me the box itself is good. Then I looked at the original arm attached to the tie rods and took the end of it thinking to move the whole assy., and the end of the arm moved a good 3/4 of an inch before moving anything else!
So Greg G. from NY was correct! The rubber bushings in the endes of the "Y" shaped steering arm are shot - deteriorated from years of absorbing oil! It is so strange that when everything was still assembled the play or movement could not be seen!
I have ordered replacements from Steel Rubber Products, although I wish these bushings were available in polyurethane.
Thanks for all of your help and suggestions, it got me started on the right path to find the problem.