This may be due to poor/cheap "new" repro parts. I have been amazed at how many parts you can get for these cars at really inexpensive prices. Unfortunately, I think the competition for lowest price drives some places to deliver substandard equipment. So in more cases that I ever expected, I found the "new parts" were fine when I brought them, but they wear out super fast, or don't work as well as originals. I wonder if you inadvertently bought inexpensive ball joints when you put them in, and they just weren't a good product? Makes me wanna go check mine - they have about 3K on them now...