ok, word from my parts guy is just what I figured, this 8j000 is the replacement for the ag000, part has been redesigned & the new part # supersedes the old... according to my guy the old ag000 is either no longer available or at least being phased out & will no longer be available after whatever is available is depleted... it seems nissan redesigned this bearing sometime in 07
now still, at this point, I don't know that we even have any real evidence that the new design isn't any good... it very well may be... usually something like this happens when they improve a design, it's obvious that according to Nissan at least, this new plastic slider bearing is better than the old ball style... that's the only reason they would update then supersede a part like this...