No it doesn't have to go back. There is a nylon spline drive that connects it to the accessory drive. It is replaceable. B&C has them. Just call them, as I don't see it on their website. It's a quick repair. Just take the SD-8 off, pull out the broken one, and replace it. These work the same way the vacuum pumps do. They are designed to fail and not hurt the engine.
Now, you might want to figure out why it broke. It might just be age. They had some weak drive splines a few years back, and changed them. I had a failure with the weak ones, but haven't had a failure with the new ones on 2 SD-8's now.
Vic