'92 2WD 3.0 Ranger Ball Joints

I'm replacing a spindle with a fairly clean looking junkyard spindle, and am wondering if anyone can help me out as far as how to tell if the junkyard spindle ball joints are bad or not. The rubber jackets look OK, but I don't really know how to tell for sure if the joints should be replaced or not. Sure would be nice to know before putting everything back together again. Thank you much.

without them installed there isn't a real good way to check them. since you already have it out i would just replace them with new ball joints. Moog brand

without them installed there isn't a real good way to check them. since you already have it out i would just replace them with new ball joints. Moog brand
Thanks, I hear that Moogs are good, but these don't look like they have anything bad about them, and I'm not sure that I want to go to the expense of replacing good ball joints if they're OK. If I don't replace them, what is the best way to grease them? Just lift up the rubber covers and slop some general purpose grease all over? Thanks again!