It looks like the old TRE looks better than the new one, what does the inside of the arm look. is it galled like the TRE is not seating? And is the circle imprint on the arm from the TRE bottoming out. Also has the castle nut always run down past the hole You mentioned needing a washer. I ended up drilling mine out and run Heims and misalignment washers and have not looked back.
What torque value are you using?
On the hardness of the arms, It seems like the hammer always leaves a mark on the arm.
Seems like the TRE's would be harder than the arms.
I also may have a set of arms I pulled off when I went to another set up. Unknown condition, but I had no issue when I pulled them.
None of this is any help, just an observation.