After everything that you have tried it sounds like you have an internal crack in valve.We have seen this many times over the last 25 years. There are plenty of salvage yards in Iowa that I would call to get a used header lift valve. I wouldn't think of spending $1200 for a new one. Check with Eiklenborg's in Aplington,IA or Teubel Salvage in Drakesville,IA. I would put the new o-rings in the used valve and you should be good to go. Hyper Harvest II
Did the second stage poppet seat on lower side fall out and was there an oring on that seat. I don't believe I have ever been able to remove the seat on that side. Don't know if they were loctited in at factory or what. I would imagine if you replaced that seat you got one from raise side and it would have oring. If you don't have cut oring or loctite that didn't dry up before putting to use I would give up and find another valve. We have had a few over the years that we had to give up on after first attempting repair. Pin hole or crack block is certainly possible.
figuring on replacing block when get rained out. going used.priced one at ac for 1500.sometime i would like to price an entire combine,including every part and piece from a dealer.what do you think it would costIJIJ
did you replace the square cut orings in the block that seals the raise and lower adjustable poppets - it is a bear to do but they will cause problems if not replaced. And there is not a removable seat on the lower side - have no idea why the designers put a seat on the raise side .