Hello, Thanks for requesting me. I will be glad to help all I can. (FYI the serial number you posted is the engine serial number, it is linked to a 6BS00399 and this should be your machine serial number.)
Are you saying the lift and tilt do not operate correctly either? If so, it could be air. If the oil appears foamy and the pump is noisy, then air is likely the issue.
Did you change the filters? Cut open old filters and inspect them for metal or other debris that may relate to a system failure.
Is the oil level correct and are you using 10W hydraulic oil? This tractor operates all transmission and hydraulic functions on this one oil. It is critical it remains clean and the correct grade.
Has anyone tested the pump pressures for the implements?
Did this tractor have any add-on attachments?
Does the 9T7249 valve have an end cover plate with plugs in it is is it blank?
Have you tried swapping the main relief from the old valve to the new valve?
This hydraulic system is fairly simple and should not have this trouble. Do you trust the hydraulic shop that tested the cylinders or the one that resealed the valve?
Do you have any testing gauges?