The balls in the right hand retainer of your picture look worn. Were those perhaps from the lower race? Examine the crown race (the headset piece on the fork) and look for damage. If you see pitting, replacing the crown race is needed.

In any case, most people replace balls whenever they service the headset; they're cheap enough. You can either pack the new balls in loose, without a retainer, or pop the old balls out of the retainer and insert new ones.