When we got the first Invader I convinced myself that I needed all the carb parts. The guy at Carb Parts Warehouse said that the gaskets on the bowls almost never go bad. He was right, we are still running the original bowl gaskets and the new ones that I bought are still sitting in the box. And for that matter, so long as you keep the carbs clean, the jets almost never need to be replaced.
Wanting to be sure that they run properly, replace the three jets and replace the needle and seat. Take out the needle jet and make sure that the reservoir is clean and clear. Clean out all the air passages with a torch tip cleaner, carb cleaner, and compressed air making sure to wear protective eyeware to keep gook and carb cleaner out of the eyes.