[72 Burb 3dr]

Two questions:

Front lower ball joint - the one I replaced was spinning when we tried tightening the castle nut back on it. The new one does not. I tried a Google search, and that seems to be common as there were multiple links about how to tighten it when it spins. Why does it spin, and is that in issue that I should just replace the joint? (I did replace the drivers side due to a bad seal, but the passenger side we just went with it because the part stores were already closed by that time).

Front rotors - I've replace inummerable brake pads on all kinds of makes and models. The only time previously that I've run into a grooved rotor is from someone running the brake pads into nothing. I thought that was the case when I removed the drivers side and found a groove running down the center of the rotor. Then I found the exact same groove down the center of the passenger side. Was that stock? Or just prior bad maintenance that coincidentally grooved both sides exactly the same?