While doing research into what type of o-rings to use:
"The continuing introduction of aggressive chemicals into power steering (and au-
tomatic transmission) fluids in recent years has created compatibility issues with many
proven seal elastomers. For example, the nitrile compound Buna N, the most resilient and
extrusion-resistant seal material ever developed (for example, after 75 years it’s still used
for the o-rings in AN fittings) is subject to shrinkage and embrittlement from contact with
most synthetic fluids. Contrary to their advertising, “performance aftermarket” synthetics
and semi-synthetics are NOT universally suitable for all power steering systems, and in many cases will prove actively destructive. So-called “anti-foaming” agents (usually just a thick-ener whose supposed foam-suppressing action consists of keeping the air bubbles suspended in the oil—exactly where you don’t want them) are another ingredient best avoided. Some other additives, such as those sold to “restore” power steering, will cause Buna N seals tolose their durometer hardness and swell beyond their dimensional tolerances. While that may help a ‘72 Buick, it is guaranteed to cause rough steering in a race car with a four-inch rack."
Here is another matierials guide, it recommends Polyacrylate or Hydrogenated Nitrile
Aflas is suggested here:
Hydrogenated Nitrile, HNBR is suggested here:
Ethylene Acrylic, Vamac® (AEM), Hydrogenated Nitrile, HNBR, Polyacrylate (ACM):
(For Type 'A' Fluid)
POLYACRYLATE from here (type A):
This link is really awesome it does a good job showing the comparisons:
The oringstore.com recommends HNBR (which is what I ended up ordering).