The replacement of the Toyota tail light assemblies is not an item that should routinely occur. There are no moving parts in them that will wear out in time, but they are sealed units and the seal must be maintained in order to protect the electrical components on its interior for the Toyota to be street legal. One reason for a Toyota owner to be repairing their tail light assembly is due to damage. When one of the bulbs has burned out, the lens must be removed and then remounted after the bulb has been replaced. Sometimes, owners over toque the lens mounting screws. This tail light assembly is only made out of plastic. The screws are metal and can easily strip the threads in the plastic out. The threads hold the mounting assembly can also be cracked because of the additional force being exerted on it. This will require the entire Toyota tail light assembly to be pulled from the vehicle and thoroughly inspected. If that is not accomplished, a crack in the assembly might go unnoticed. This crack can allow moisture to enter the assembly causing the bulb to short out. When replacing the bulb that has burn out, it is also a good idea to inspect the seal where the lens and the housing unit are joined together. This might be the reason the bulb burnt out if there is a break in this seal that permitted moisture to enter the tail light housing unit. The eyes of the inspector are the best and only way to know if the tail light assembly on your Toyota is in proper working condition. Its only task is to prevent moisture from entering so the electrical components can stay dry.