What exactly goes wrong with an AOS?

[Padawan]

I'm in the process of working on what may be an air/oil separator related issue. My question, though, is what goes "bad" on one of these? I'm aware of the bellows and J-tube connectors that can crack and leak, but assuming that the AOS itself is not physically broken, what causes it to need replacing? My reading seems to indicated that it's essentially just a plastic container with a series of baffles and chambers inside. Granted, it's not terribly expensive, but why can't this unit just be cleaned out thoroughly and re-installed? Is there something else I'm missing, like some moving part or internal filter media?