Hi Chev thank you for the ideas. So you have had one of these cessna's apart? Mine will come apart easy now that it has been apart once. When I picked it up he told me to go ahead and take it apart again if I wanted to see how it was made. Unfortunately i was not in the shop when they figured out how to get it apart. So I don't know how tight the spool fit in there. I'm guessing that there should not be a lot of clearance between the spool and the bore?
I'm going to try my test with the piston rod disconnected from the frame of the tractor to see it actually cycle in/out. I think I'll end up taking the cessna apart again. I like your idea of using a shim between the orings and the bore. I've got some pretty thin plastic sheet that I used when I installed some oil seals in a transaxle on my 853. You really have me wondering if there is a ripped oring or something.
One note, before I took the cylinder off of the cessna control valve I could put my fingers over the in and out ports on the cessna and could cycle the piston rod in/out with almost no resistance. That told me there was an issue internal somewhere. I should not be able to move that rod if the control valve ports are blocked off. After I remove the complete unit I will try that test again before I take the cessna apart. I did not try that test before I installed it because there was no oil in it and I did not want to damage anything.
I like the thoughts of knowing that an HT series setup will work on here. I doubt I'll ever pursue that as the price of a 2nd power steering for this tractor would not be worth it. Well thanks for all your thoughts on this I will keep you posted.