I use Lucas.
I became a Lucas fan when I had an old Corvette. It developed a sort of hard spot in the steering when turning left. Just when I decided to sell it, it started leaking power steering fluid also. When in an auto parts store I noticed that Lucas power steering stop leak says "Will stop all leaks and steering hard spots or your money back" I thought that was such an amazing claim that I had to try it. One bottle and the leak stopped and the hard spot was gone. I will never understand it but it made me a believer in Lucas.