This is an old post, but yes I did the adjustment. I had an intermittent clunk going on. Someone else on here posted about this adjustment but I can't seem to find it. Anyway, just remove the plastic oil drip guide from the cross member and you can get access to the bolt - I hear some are hex head and some are external Torx. I slipped on a standard socket (size escapes me at the moment) and tightened it maybe 1/8 turn. I drove it and the clunk was gone but the steering was too tight (wheel did not return to center after turning). Went through this a few times until it felt right, but it did indeed fix my steering clunk. Go easy on the adjustment - less is more.
2006 XK Sport, Midnight Blue
4.7L, 4x4, tow package