Onan carburetor float has fuel inside of float

The plastic ones, over time deteoriate, especially if alcohol, is in the fuel.
Perhaps floats of the last few years are better. Onan has been around a while perhaps one of their dealers has a kit with brass float. Alcohol will attack it too but less than old plastics.
Onan doesn't make it's carbs. It buys from a supplier, I would think. Perhaps you can find a number on it and find a float or kit with brass float,on the Internet.
Don't lose sleep trying to find one though.