If there is any avenue for helium to leak then some will be expelled as the inside of the disk gets hot. It will then float away in the denser air.
When the disk cools again the same avenue could be too small for air to be sucked back in. The pressure inside the disk will be lower - but will still be uncontaminated helium.
That process probably occurs at some factory initial burning in stage - so wouldn't be repeated in a user environment unless the disk gets hotter.
Whether it would eventually keep leaking due to Brownian motion - and keep reducing the internal pressure - is one for the physicists.
If the escape avenue also allows air to enter then the helium inside will be contaminated over time - even if only by Brownian motion.
Biting the hand that feeds IT
