I use Amsoil synthetic ATF in my Western plow, on the 2nd winter with it in there.
I don't see any benefit to using an ATF+4 fluid though but the synthetic made a big difference in my plow. I don't hear any groan in cold weather any more.
I just called one of my ROTS, his primary business is a Boss/Western dealer/installer (for years), he says Dexron ATF (GM) and does not recommend the other fluids.
[ January 18, 2006, 12:07 PM: Message edited by: Mike ]