I would check your control valve gaskets for breaks or missing pieces before I would be pulling the transmission out. One thing I have done frequently is remove the control valve and find the port for the forward clutch on the mounting case. Use a rubber tipped air blower and see if it will hold air pressure. If you hear air rushing inside the transmission then you know its likely blown piston seals, tube line orings, or a split tube line itself.
Clarify control valve . I removed the clutch control valve assembly and replaced all the valves I could and the piston . Everything seemed to be working correctly . I did not test or replace any springs. Another advisor suggested as you did about air pressure into the forward port. I was hoping to do that in the next day or so. Thank you.
This would be my next move.
