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Helium isn't a long term thing - it's notoriously hard to keep behind a seal as the molecule size is tiny. That's why they normally use argon as the purge gas - it's a much bigger particle size so...

Was about to say the same thing as m101a1, but thought I's better just read to the bottom haha... Dry internals is the key, doesn't matter if the thing is gassed on argon nitrogen or whatever in...