power steering

The diagnosis is that the power steering on your car is a POS. First off, there is a lot of slop in these things....from the factory. (That's just how they were designed) Second, these things are notorious leakers.....almost from the factory. Third, they are somewhat expensive to repair and few people will even try to fix these. Now with that being said, you will probably want to get it going again just because it's original and you GOTTA have it. I think there are a few places that will rebuild these for you even if you have to send it off to have it done. Google Mustang power steering for starters. Oh, BTW. The problem on your car (probably) is that these setups have a valve that directs oil one way(right turn) or the other way. (left turn) It sounds like your setup is stuck in one direction or somebody that doesn't know squat tried to fix it. After what happened to yours, are you ever going to trust getting it fixed and driving it with it (marginally) working again?

If it's the valve, and it sure does sound like it is, a number of vendors are now selling rebuilt valves, and I think I just saw one which is advertising brand new aftermarket valves. Which ones, off hand I do not recall, but I would start with Mustangs Plus

Of course, if you are not going concours, this might be the perfect time for that rack and pinion mod.... : 0 )

Bad power valve. Could be completly shot, or just maladjusted.

If you're doing a complete restoration, you'll have to spend big bux on restoring the steering. Lines, hoses, power valves, boxes, etc. Very expensive for mediocre 50 year old technology. If it's not a restoration, get a power R&P kit, like Steeroids. Actually less money, and a much better product. Total Control is also very good, but very expenive. DO NOT get the flaming river manual steering kit.

Any particular reason regarding the FR unit?