Did something fall off my bike?

[Grumpy Goat]

Whatever it is (was), mine's gone missing too!
I'm guessing some extra bore in the case for some other model?
At first, the plastic piece looked like a gasket.

Whew! That is good to know that yours and Darrell's bikes have the same arrangement. Agree that it might we there for some other model. Kind of crappy to keep the gasket there flopping around and doing nothing, though.