Question, was the wheel ever hit, like sliding in the ice/snow? I saw at my work, not the same but just brainstorming, the link had fallen off, it was easy to turn one way, but harder to turn the other. I would assume that it would apply if it was bent too.
However, I think that your troubleshooting has led to the most likely culprit, a blocked valve. I'll have to take a look around to see what I can pull up. I am not sure of what valves are used for our cars, but nothing a little hydraulic knowledge can't help with.
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