If you are running the factory controller, one bad glowplug and you are not going anywhere. The factory controller will not glow the plugs long enough with one bad glowplug. The engine will start with 2 or 3 bad glowplugs if you are using a manual button.How long do glow plugs usually last? Is there a recommended replacement interval? Or do you wait for one or more to fail, then change all eight...