If things are as bad as portrayed in this thread than the only way to fix it would be to fire all the balance team and make them apply (together with everyone else again).
And regarding the churn - that is perfectly fine, all the members are free to put down their torches at any time at which point the team lead will call for new members.
If however members become inactive then they will get the boot (you cannot maintain a crucial role in any organization for the prestige of that role alone)
Perhaps you could make a list of past contributers so that their assistance is acknowledged or something but the activity requirement should be non negotiable.
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