<font color="blue">But, the dealer put the fear in me when he told me a bunch of stories about brakes chattering, transmissions failing, warranties being denied, etc.</font>
Any oil that meets the NH134D specs is fine. I've been running Amsoil Hyd fluid for months and about 25 operating hours without a problem.
<font color="blue">It might have been a bunch of BS, but it did get me thinking that I need to find a cheap source of real NH 134D.</font>
It is a bunch of BS and if he got you thinking about not buying another brand of fluid he has achieved his goal. There's nothing wrong with using NH134D, or any other fluid that meets NH's specs. There is however something wrong with this dealer. He's not being honest with you.
I would push the dealer and ask for the names of the people who had these problems, and proof that it was a direct result of using other than NH fluid. My NH dealer also sells Kubota tractors and if a NH tractor owner wants to use a synthetic hyd fluid, he uses Kubota's SUDT.