power steering pump problem

You can find steering fluid for early Mopars (pre-1985?) when lucky. My later Mopars specify ATF fluid. I don't know why it matters. I put synthetic power steering fluid in my 65 Dart. I forgot the brand - Red something?, and couldn't find any more of it. I recall buying it at Tognotti's speed shop. However, many fluids labelled "synthetic" is just marketing hype, like in brake fluids.