Okey,so let's step back and take a recap here... You've stripped and cleaned the whole unit, and also stripped and cleaned the Valve.
Then, you tried the valve on another unit and it works as it should, but back on the original machine and it's not working.
Have you checked for obstructions stopping it from opening? Such as a small bit of debris, perhaps it's not fitted quite right?
Have you done the opposite and tried the working Valve from the unit you tried this one in, on the original unit? Does that work?
I'll await your reply while sipping Whiskey and sitting in my arm chair.