Was just into that a couple of days ago, and mine look like that as well, only with deeper grooves. (but I remember they already were grooved last time, so it might be old news)
So - same question. Is the groove a problem?
Was wondering if replacement is a good idea?
No signs of any other issues on mine.
Spindle surface step (from inner bearing race spin wear) - barely able to feel.
Bearings - smooth.
In fact, the whole adjustment nut preload thing was a question because the bearing are so smooth.
With the adjustment nut way over-tightened (for grease squeeze out), could spin the tire with just one finger.
So, basically, nothing to judge how tight to go.
So I "tightened by feel" (guessed), and took it out on the freeway for 15 miles or so on a cool evening - hubs mildly warm - OK I guess.
Have the feeling a little tighter wouldn't hurt?