Just curious, mine rotor is a little burnt, and the caps electrodes are slightly corroded at the contact point.... but do you normally just change it when the cap is cracked? Or is there another way to tell when to replace (with looking at it, not miles)

 

oxidation/corrosion and cracks are the best indicators, whether on the cap or the ignition coil inside it.

 

preventative maintenance means you change stuff before it breaks down on you, if you went so far as to screw them off, just change them. i think they were like 30-40 bucks conbined from autozone