Power Steering Fluid: use PS fluid, or Dextron ATF?

[cheepyankee]

My PS fluid is about 5 years old, a little dark, so I figured drain the resiviour, and add clean stuff. Only AFTER refilling with regular Power Steering Fluid, did I see on the cap it says to use Dextron ATF.

ATF? WTF! Is this bad? Should I just leave it, or drain the whole system and add Dextron? TIA