The "front differential oil" should be ignored. That is the same as the transaxle ATF. Regarding the transaxle drain and fill plug washers, you are supposed to replace them each time the plugs are removed. However I think it is safe to reuse them at least once, perhaps more if you want to save the cost of new washers. The fuel line runs from the fuel tank up to the engine compartment. If you don't smell gasoline fumes I would not worry about that. Inspect the radiator, engine coolant pump, and hoses for leaks, you would see pinkish or whitish stains. Inspect the air conditioner plumbing for oil leaks. No pressure gauge is required. The Prius does not have a supercharger so there is no intercooler. Another example of the poor editing of that generic list.