Could someone tell me when can you tell when the upper control arms go bad in a 99 GS-300? Mind are very rusty from several years of driving like 5 years.

 

rust is not a cause for replacement unless it is threatening the structural integrity of the arm...What you are looking for is movement / play in the bushings and ball joint... basically, with the car off the ground, grab the wheel and tire and try to deflect it - push in at the top, pull out at the bottom and alternate pushing and pulling - watch the ball joint and where the control arm bushings attach to the cars chassis - there should be zero movement in the ball joint, and just a hair of flex in the bushings... anything more and replace it/ them...