After oil change at a garage I discover when steering got squeaky that cap was off my PS fluid and I've lost quite a bit. Is there a reason I would buy one PS fuuid over another other than brand choice (are they all the same no matter the vehicle?) and what might I need to know as far as how full or when to add it? Cold car? Warm car? I have 1997 Ford F150 2WD

You need to check on the actual power steering cap to see just what is recommended for your vehicle. They are not all the same and you could end up using the wrong fluid. There is a level indicator on th actual dip stick that says cold and hot. Take out the stick and look at it carefully and you'll see the markings. Do not overfill ever!

You can really use any brand, I use transmission fluid in mine.does the same thing. Just don't put power steering fluid in your tranny...

Ford recommends Mercon ATF. Don't add too much. When the engine is hot, the level should not exceed the MAX Line. When cold, fill the reservoir about 1/4" below the MAX Line. I recommend (and use) Mobil 1 Synthetic Multi-Vehicle ATF in the power steering unit of my Ford Taurus. It's available at WalMart and will greatly improve the performance and life of your power steering unit.