You may have a broken spring in your upper king pin. I would just buy a new pair of springs & nylon bushings and install them -- they aren't too expensive, and once you have the cap & steering arm off for inspection, you might as well replace them. It is pretty unlikely that you have trouble with the lower pins.

BTW: Rock Auto has moog adjustable caster/camber kits that replace the actual lower pin/plate assembly. IMO it is the best adjustment kit available, and addresses the unlikely case of replacing a pin worn by a stuck bearing . . .