Hey, that's a pretty danged good idea. Why didn't I think of that? (On second thoughts, don't answer that question...)
maybe you are the one who could test the reliability of the second o-ring: Remove the yellow main o-ring and use the second o-ring alone on a deep and a shallow dive. Then check the battery compartment.
I don't feel any need for those knob extenders, despite using either 5mm gloves or drygloves, so some 20€ is a bit much for an O-ring. But I'll look around for a suitable O-ring at a decent price, and if I find one I'll do that experiment.
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