The axle shafts on your 300ZX take the biggest beating on your car. Overtime, the constant torque from hard driving and hard launches wear the joints the until eventually, they break leaving you stranded. It is also common for the grease boots to crack allowing dirt and other contaminates into the joints, and letting the grease out causing excessive wear on the joints and premature failure. Don't wait until they break, inspect and replace your damaged axles today!