They are not totally sealed, but you can not get into them from the top. The shaft does seal fairly well, so just spraying into them from the top won't do much (faders excepted of course)
You can get to the back of the pots and get into them at the crimp point. It's definitely a pain to get there, and will require some disassembly to get to the boards.
Sorry to give a response to an actual hardware question .. I'm sure someone will fill in and bring this back on-topic.. all distorted politics, all the time.
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Ahh ... some dick DID change my tag line again.