I don't know if the Tube was ever OEM, so having one (used boat?) might indicate the bellows have been changed. As Bill said, Exhaust Bellows isn't critical. Drive Bellows leaks damage the U-Joints, Input Shaft Yoke and Seal, and Gimbal Bearing. They don't let all that much water into the Boat. According to BoatUS, Shift Bellows are a major cause of I/O boats sinking at the dock. Water enters the boat in a steady pencil-sized stream. It also lets water into the Lower Shift Cable. This causes balky shifting AND the Shift Interrupt Switch on Alpha One's to operate when it isn't designed to. When that happens the engine quits.
Changing Bellows? ALSO change the Trim Indicator/Trim Limit Sender/Switch Kit! Another $70 or so, but little to no additional labor.