I was told that it is okay to use ATF when in a bind to put into a power steering pump, that both fluids are hydraulic. Is this true? Will it damage my power steering pump?

 

If no PS leak, then no need to add any. Why would PS fluid be tough to obtain ???

 

Look at this video link. Have a leak, fix the leak, using the wrong fluid can cause other issues in the system costing you more money and time.
You can go the Chevy's site to pull up your owner's manual if you don't have it.

 

No, ATF is a 10 weight lubricant. It is safe to use in a GM power steering pump.

I recommend using a synthetic fluid such a Redline or Royal Blue power steering fluid, but regular ATF has been used for years in GM vehicles power steering pumps.

The best thing you can do is replace it with a suction device, and fill it up with whatever ATF or other fluid recommended, as it does wear out of additives and can also accumulate debris from the wear and tear on the pump, or dust from the outside.